Handling a UE and timers associated with the UE during an unavailability period

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. Embodiments herein provide a method and a system for handling a UE (102) and timers associated with the UE (102) during an unavailability period.

Description

HANDLING A UE AND TIMERS ASSOCIATED WITH THE UE DURING AN UNAVAILABILITY PERIOD

[0001] The present disclosure is related to wireless communication. More particularly, the present disclosure is related to a method and system for handling a user equipment (UE) and timers associated with the UE during an unavailability period in a wireless communication system.

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The unavailability period of the UE refers to the time duration during which the UE is unable to access the network services. For instance, the UE may enter into an unavailability period due to various reasons, due to software upgrade in the UE, or loosing satellite coverage. When the UE activates an unavailability period, it sends a registration request or a deregistration request to an access and management function (AMF) to indicate how long it will not be available. The UE cannot connect to the network while an unavailability period is activated successfully until the UE trigger to exit the unavailability. The NAS state of the UE (5GMM State) is currently solely described by the state of the art and is either 5GMM-REGISTERED.NO-CELL-AVAILABLE if unavailability is activated through registration procedure or 5GMM-DEREGISTERED.NO-CELL-AVAILABLE if unavailability is activated through registration. Since the UE's AS layer is still active, it will carry out its regular operations like cell selection / cell reselection, choose a new cell based on the available information at AS layer, and indicate to the NAS layer with necessary information (for instance, when AS layer reselect to new cell, it indicates to the NAS layer about the attributes of the cell like tracking area identifier, cell identifier etc.). Suppose, the UE moves to the TAI where the current TAI is not in the list of tracking areas that the UE previously registered in the AMF. As a result, even if the UE is still unavailable, it could start the registration process which cause exiting of UE unavailability period.

[0009] Furthermore, in cases when the AS layer is still active, the UE may start the registration process while it is unavailable (i.e. unavailability period is active). This would make the UE available on the network side and let it to start any network-initiated processes, such as data connections and paging, even while it is still unmatched and cannot manage it. While the UE　is unavailable, the UE may also transmit NAS messages to the network. The UE performs AS-related operations when the AS layer is kept active throughout the unavailability period, which might result in excessive battery usage.

[0010] Further, when the UE is in the unavailability period, the network (for example, AMF, MME, etc.) may determine the value of certain timers to be provided to the UE. For example, the timers may include a periodic registration update timer (T3512) or a periodic tracking area update timer (T3412) or the negotiated extended DRX parameters or a timer T3324 or the extended idle mode DRX cycle parameters or the PSM mode configuration parameters. For instance, the value of the timers may be determined based on the unavailability period duration and the start of the unavailability period, if available. However, the network does not consider the discontinuous coverage maximum time offset value, which is given to the UE when considering or determining the timer values. If the network has indicated a non-zero discontinuous coverage maximum time offset to the UE earlier and the discontinuous coverage maximum time offset timer is still running in the UE with a non-zero value, the periodic timer T3512 / T3412 may expire. Thus, there is also a need of a solution to handle timers associated with the UE while the discontinuous coverage maximum time offset timer is still running.

[0011] Hence, is desirable to address the above mentioned problems and disadvantages or at least provide a useful alternative.

[0012] The principal object of the embodiments herein is to handle the UE during an unavailability period in a wireless communication system

[0013] Yet another object of the embodiments herein is to deactivate the AS layer of the UE when the unavailability period of the UE is activated. This causes the AS layer to stop performing any AS layer related procedures

[0014] Yet another object of the embodiments herein is to activate the AS layer only when the UE comes out of the unavailability period. Once the AS layer is activated, the UE initiates the registration procedure.

[0015] Yet another object of the embodiments herein is to handle timers associated with the UE during the unavailability period in wireless communication networks.

[0016] Yet another object of the embodiments herein is to enable the network / AMF / MME to adjust at least one of the periodic registration update timer (or Timer T3512), the periodic update timer, the periodic registration timer or periodic TAU timer (Timer T3412), the mobile reachable timer, the implicit de-registration / detach timer value, an T3412 Extended Value or an extended T3412 timer, a plurality of negotiated extended DRX parameters, a plurality of extended idle mode DRX cycle parameters, an active Timer (T3324), a MICO mode (Mobile initiated connection only) configuration timer, an extended connected time, a plurality of Power saving mode (PSM) mode configuration parameters, T3324 Extended Connected time timer and the maximum time offset value so that the UE is not de-registered / detached by the AMF / MME / network or the UE and the Network (for e.g. AMF / MME) are in sync regarding the Unavailability period handling, registration / Attach status and the power saving status of the UE .

[0017] Yet another object of the embodiments herein is to enable the UE to trigger the mobility registration update (MRU) while the MM BO is running.

[0018] Yet another object of the embodiments herein is to enable the network to adjust the MM BO in such a way that the UE can trigger the MRU as the MM BO finishes before a discontinuous coverage (DC) starts.

[0019] Yet another object of the embodiments herein is to enable the UE to trigger the MRU (normal), and the network to adjust the MM BO in such a way that the UE does not detach.

[0020] Yet another object of the embodiments herein is to prevent the network in performing a rejection when the UE indicates an unavailability period.

[0021] Yet another object of the embodiments herein is to enable the network to perform a rejection in such a way that the UE does not detach, when the UE indicates an unavailability period.

[0022] In one aspect, the objectives are achieved by providing a method for handling a user equipment (UE) during an unavailability period in a wireless communication system. The method includes detecting whether the unavailability period has been activated by the UE through a registration procedure between the UE and an access and mobility managements function (AMF) apparatus. Further, the method includes deactivating an access stratum (AS) layer of the UE when the UE is currently in the unavailability period (i.e. UE successfully activated unavailability and currently unavailable). Further, the method includes determining whether the UE has come out of the unavailability period. Further, the method includes activating the AS layer of the UE when the UE come out of the unavailability period. In addition, the method includes transmitting a registration request message for registration procedure for mobility and periodic registration update to the AMF apparatus for initiating the registration procedure upon activation of the AS layer.

[0023] In an embodiment, the method includes detecting whether the unavailability period has been activated by the UE through a de-registration procedure between the UE and the AMF apparatus. Further, the method includes determining whether the UE come out of the unavailability period. Further, the method includes activating the AS layer of the UE when the UE come out of the unavailability period. In addition, the method includes transmitting a registration request message to the AMF apparatus for initiating the registration procedure for initial registration upon activation of the AS layer.

[0024] In an embodiment, the UE comes out of the unavailability period only when the AS layer is deactivated.

[0025] In an embodiment, the UE performs the registration procedure for initial registration when the UE comes out of the unavailability period, and the unavailability period is activated through the de-registration procedure.

[0026] In an embodiment, the UE performs the registration procedure for mobility and periodic registration update when the UE comes out of the unavailability period, and the unavailability period is activated through the registration procedure.

[0027] In an embodiment, the UE activates the unavailability period using the registration procedure and deactivates the AS layer only after the unavailability period has been activated.

[0028] In an embodiment, the UE activates the unavailability period using the de-registration procedure and deactivates the AS layer only after the unavailability period has been activated.

[0029] In one aspect, the objectives are achieved by providing a method for handling timers associated with a user equipment (UE) during an unavailability period in a wireless communication system. The method includes receiving, by a network apparatus, unavailability information from the UE through a registration procedure between the UE and the network apparatus. The unavailability information includes at least one of a start of the unavailability period, an unavailability period duration, and an unavailability type. Further, the method includes determining, by the network apparatus, a discontinuous coverage maximum time offset for the UE. In addition, the method includes determining, by the network apparatus, a value of a plurality of timers associated with the UE based on the discontinuous coverage maximum time offset for the UE determined.

[0030] In an embodiment, the plurality of timers include a periodic tracking area update timer (T3412), an T3412 Extended Value or an extended T3412 timer, a mobile reachable timer, an implicit detach timer, a periodic registration update timer (T3512), an implicit de-registration timer, a plurality of negotiated extended DRX parameters, a plurality of extended idle mode DRX cycle parameters, an active Timer (T3324), a MICO mode (Mobile initiated connection only) configuration timer, an extended connected timer, a plurality of Power saving mode (PSM) mode configuration parameters, and a T3324 Extended Connected time timer.

[0031] In an embodiment, the unavailability type is set to unavailability based on the discontinuous coverage.

[0032] In an embodiment, the network apparatus can be one or more of an AMF, an MME or a Network function or a Network entity.

[0033] In an embodiment, the method includes, performing one or more of: handling the plurality of timers based on the start of the unavailability period, the unavailability period duration, and the discontinuous coverage maximum offset; and adjusting the discontinuous coverage maximum offset, based on a pre-determined plurality of timers, the start of the unavailability period, and the unavailability period duration.

[0034] In one aspect, the objectives are achieved by providing a user equipment (UE) for handling during an unavailability period in a wireless communication system. The UE includes a memory, a processor, and a controller communicatively coupled to the memory and processor. The controller detects whether the unavailability period has been activated by the UE through a registration procedure between the UE and an access and mobility managements function (AMF) apparatus. Further, the controller deactivates an access stratum (AS) layer of the UE when the UE is currently in the unavailability period. Further, the controller determines whether the UE has come out of the unavailability period. Further, the controller activates the AS layer of the UE when the UE come out of the unavailability period. In addition, the controller transmits a registration request message to the AMF apparatus for initiating the registration procedure for mobility and periodic registration update upon activation of the AS layer.

[0035] In an embodiment, the controller detects whether the unavailability period has been activated by the UE through a de-registration procedure between the UE and the AMF apparatus. Further, the controller determines whether the UE come out of the unavailability period. Further, the controller activates the AS layer of the UE when the UE comes out of the unavailability period. In addition, the controller transmits a registration request message to the AMF apparatus for initiating the registration procedure for initial registration upon activation of the AS layer.

[0036] In an embodiment, the UE comes out of the unavailability period only when the AS layer is deactivated.

[0037] In an embodiment, the UE performs the registration procedure for initial registration when the UE comes out of the unavailability period, and the unavailability period is activated through the registration procedure.

[0038] In an embodiment, the UE performs the registration procedure for mobility and periodic registration update when the UE comes out of the unavailability period, and the unavailability period is activated through the registration procedure.

[0039] In an embodiment, the UE activates the unavailability period using the registration procedure and deactivates the AS layer only after the unavailability period has been activated.

[0040] In an embodiment, the UE activates the unavailability period using the de-registration procedure and deactivates the AS layer only after the unavailability period has been activated.

[0041] In one aspect, the objectives are achieved by providing a network apparatus for handling timers associated with a user equipment (UE) during an unavailability period in a wireless communication system. The network apparatus includes a memory, a processor coupled to the memory, and a timer controller communicatively coupled to the memory and the processor. The timer controller receives unavailability information from the UE through a registration procedure between the UE and the network apparatus. The unavailability information includes at least one of a start of the unavailability period, an unavailability period duration, and an unavailability type. Further, the timer controller determines a discontinuous coverage maximum time offset for the UE. In addition, the timer controller determines a value of a plurality of timers associated with the UE based on the discontinuous coverage maximum time offset for the UE determined.

[0042] In an embodiment, the plurality of timers include a periodic tracking area update timer (T3412), an T3412 Extended Value or an extended T3412 timer, a mobile reachable timer, an implicit detach timer, a periodic registration update timer (T3512), an implicit de-registration timer, a plurality of negotiated extended DRX parameters, a plurality of extended idle mode DRX cycle parameters, an active Timer (T3324, a MICO mode (Mobile initiated connection only) configuration timer, an extended connected timer, a plurality of Power saving mode (PSM) mode configuration parameters, and a T3324 Extended Connected time timer.

[0043] In an embodiment, the unavailability type is set to unavailability based on the discontinuous coverage.

[0044] In an embodiment, the timer controller performs one or more of: handles the plurality of timers based on the start of the unavailability period, the unavailability period duration, and the discontinuous coverage maximum offset; and adjusts the discontinuous coverage maximum offset, based on a pre-determined plurality of timers, the start of the unavailability period, and the unavailability period duration.

[0045] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications be made within the scope of the embodiments herein.

[0046] According to an embodiment of present disclosure, methods and apparatus to handle efficiently a terminal during an unavailability period in a wireless communication system are provided.

[0047] These and other features, aspects, and advantages of the present embodiments are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0048] FIG. 1 is a sequence diagram that illustrates an unavailability through a registration procedure according to the prior art;

[0049] FIG. 2 is a sequence diagram that illustrates the unavailability through a de-registration procedure according to the prior art;

[0050] FIG. 3 is a scenario diagram that illustrates a scenario in which the UE is de-registered / detached by the network apparatus according to the prior art;

[0051] FIG. 4 is a block diagram that illustrates a schematic of a user equipment (UE) implemented to carry out the disclosed subject matter according to an embodiment as disclosed herein;

[0052] FIG. 5 is a block diagram that illustrates a schematic of the network apparatus implemented to carry out the disclosed subject matter according to an embodiment as disclosed herein;

[0053] FIG. 6 is a sequence diagram that illustrates the unavailability through a registration procedure according to the embodiment as disclosed herein;

[0054] FIG. 7 is a sequence diagram that illustrates the unavailability through the de-registration procedure according to the embodiment as disclosed herein;

[0055] FIG. 8 is a scenario diagram that illustrates a scenario in which the UE is not de-registered / detached by the network apparatus according to the embodiment as disclosed herein;

[0056] FIG. 9 is a flow diagram that illustrates a method for handling the UE during the unavailability period through the registration procedure according to an embodiment as disclosed herein;

[0057] FIG. 10 is a flow diagram that illustrates a method for handling the UE during the unavailability period through the de-registration procedure according to an embodiment as disclosed herein; and

[0058] FIG. 11 is a flow diagram that illustrates a method for handling timers associated with the UE during the unavailability period according to an embodiment as disclosed herein.

[0059] It may be noted that to the extent possible, like reference numerals have been used to represent like elements in the drawing. Further, those of ordinary skill in the art will appreciate that elements in the drawing are illustrated for simplicity and may not have been necessarily drawn to scale. For example, the dimension of some of the elements in the drawing may be exaggerated relative to other elements to help to improve the understanding of aspects of the invention. Furthermore, the elements may have been represented in the drawing by conventional symbols, and the drawings may show only those specific details that are pertinent to the understanding the embodiments of the invention so as not to obscure the drawing with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

[0060] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with a plurality of other embodiments to form new embodiments. The term "or" as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples are not be construed as limiting the scope of the embodiments herein.

[0061] As is traditional in the field, embodiments are described and illustrated in terms of blocks that carry out a described function or functions.　These blocks, which referred to herein as managers, units, modules, hardware components or the like, are physically implemented by analog and / or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits, and the like, and optionally be driven by firmware and software. The circuits, for example, be embodied in a plurality of semiconductor chips, or on substrate supports such as printed circuit boards, and the like.　The circuits constituting a block be implemented by dedicated hardware, or by a processor (e.g., a plurality of programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the embodiments be physically separated into two or more interacting and discrete blocks without departing from the scope of the proposed method.　Likewise, the blocks of the embodiments be physically combined into more complex blocks without departing from the scope of the proposed method.

[0062] The accompanying drawings are used to help easily understand various technical features and it is understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the proposed method is construed to extend to any alterations, equivalents and substitutes in addition to those which are particularly set out in the accompanying drawings. Although the terms first, second, etc. used herein to describe various elements, these elements are not be limited by these terms. These terms are generally used to distinguish one element from another.

[0063] FIG. 1 is a sequence diagram that illustrates an unavailability through a registration procedure according to the prior art. As shown in the sequence diagram, a user equipment (UE) (102) is in communication with an access and management function (AMF) apparatus (104). The UE (102) further includes a non-access stratum (NAS) layer (102A) and an access stratum (AS) layer (102B).

[0064] At step S1, an event of a trigger unavailability period occurs in the UE (102). The UE (102) shares a registration request to the AMF apparatus (104). The registration request includes an unavailability period duration in the Unavailability information IE (information element). At step S2, the AMF apparatus (104) transmits a registration accept message to the UE (102) upon acknowledgement of the registration request. At step S3, the UE (102) enters UE enters 5GMM-REGISTERED.NO-CELL-AVAILABLE state. At step S4, the AS layer (102B) is still active, due to which the UE (102) continues to camp on the cell. Also, in case the UE (102) move to other cell, the UE (102) indicates a cell indication to the NAS layer (102A).

[0065] At step S5, the AS layer (102B) indicates a service or any other indication related to camping. For example, when the UE (102) enters a forbidden TAI, the UE (102) will enter state GMM-REGISTERED.LIMITED-SERVICE or based on other indication, the UE (102) may go to a different state and does not maintain 5GMM-REGISTERED.NO-CELL-AVAILABLE. For example, the UE (102) enters a new TAI not in the TAI list. The UE (102) initiates the registration procedure. This will cause the UE (102) to exit unavailability period. This will occur if the UE (102) has not included unavailability period or extended the unavailability period when the UE (102) indicates it. The AMF apparatus (104) doesn't expect another unavailability period when already in the same state.

[0066] An event is triggered in the UE (102) making it unavailable for a certain period of time. The UE (102) supports, 5GMM and 5GSM context saving in USIM or non-volatile memory. The UE (102) activates the unavailability period using the registration procedure.

[0067] The UE (102) enters 5GMM-REGISTERED.NO-CELL-AVAILABLE. The AS Layer (102B) is already active and the NAS Layer (102A) only changed its state. The AS layer (102B) will continue to send the cell / TAI / PLMN information to the NAS Layer (102A). If the AS Layer (102B) indicates a change in cell with service with the current TAI (camped TAI) in the TAI list, the UE (102) will enter 5GMM-REGISTERED.NORAL-SERVICE. If the UE (102) received indication from the AS Layer (102B) that it has moved to TAI (not in the TAI list), then the UE (102) will initiate mobility and periodic registration. The UE (102) is not supposed to initiate the registration procedure unless it comes out of the unavailability period. Here, it is caused by the AS layer (102B) sending an indication to the NAS layer (102A).

[0068] FIG. 2 is a sequence diagram that illustrates the unavailability through a de-registration procedure according to the prior art. As shown in the sequence diagram, the UE (102) is in communication with the AMF apparatus (104).

[0069] At step S1, an event of a trigger unavailability period occurs in the UE (102). The UE (102) shares a deregistration request to the AMF apparatus (104). The deregistration request includes an e unavailability period duration in the Unavailability information IE. At step S2, the AMF apparatus (104) transmits a deregistration accept message to the UE (102) upon acknowledgement of the deregistration request. At step S3, the UE (102) enters 5GMM-DEREGISTERED.NO-CELL-AVAILABLE state. At step S4, the AS layer (102B) is still active, due to which the UE (102) continues to camp on the cell. Also, in case the UE (102) moves to another cell, the UE indicates a cell indication to the NAS layer (102A).

[0070] At step S5, the AS layer (102B) indicates a service or any other indication related to camping. For example, if the AS layer (102B) indicates cell information, the UE (102) will move to 5GMM-DEREGISTERED.NORMAL-SERVICE or any other state. The UE (102) can initiate an initial registration procedure. This will cause the UE (102) to exit the unavailability period if the UE (102) has not included the unavailability period or extended the unavailability period. The AMF apparatus (104) doesn't expect another unavailability period when already in the same state.

[0071] An event is triggered in the UE (102) making it unavailable for a certain period of time. The UE (102) doesn't supports, 5GMM and 5GSM context saving in USIM or non-volatile memory. The UE (102) activates the unavailability period using the deregistration procedure. The UE (102) enters 5GMM-DEREGISTERED.NO-CELL-AVAILABLE. The AS layer (102B) is already active and the NAS layer (102A) only changed its state. The AS layer (102B) will continue to send the cell / TAI / PLMN information to the NAS layer (102A). The AS layer (102B) indicates a service or any other indication related to camping. The UE (102) is not supposed to initiate the registration procedure unless it comes out of the unavailability period. Here, it is caused by the AS layer (102B) sending an indication to the NAS layer (102A).

[0072] In an embodiment, when the UE (102) and network support unavailability period and an event is triggered in the UE (102) making it unavailable for a certain period of time. The UE (102) may store its 5GMM and 5GSM context in USIM or non-volatile memory to be able to reuse it after the unavailability period.

[0073] In an embodiment, to activate the unavailability period, the UE (102) provides an unavailability period duration in the Unavailability information IE during the registration procedure or during the de-registration procedure (see 3GPP　TS　23.501　[8] and 3GPP　TS　23.502　[9]). The support for the unavailability period is negotiated in the registration procedure. If the UE (102) provided an unavailability period duration in the last registration procedure or de-registration procedure, the AMF apparatus (104) considers the UE (102) unreachable until it re-registers for a normal service without providing an unavailability period duration. During the registration procedure, the AMF apparatus (104) may determine the value of the periodic registration update timer (T3512) provided to the UE (102) based on the unavailability period duration. The AMF apparatus (104) releases the N1 signalling connection after the completion of the registration procedure in which the UE (102) provided an unavailability period duration.

[0074] In an embodiment, if the UE (102) supports MUSIM and is registered with support during the unavailability period, then the UE (102) can indicate a different unavailability period to each registered network.

[0075] In an embodiment, the UE (102) has stored a discontinuous coverage maximum NAS signalling wait time as described in sub clause　5.4.4.3,　5.5.1.2.4, and　5.5.1.3.4, upon returning in coverage after being out of coverage due to discontinuous coverage. The UE (102) sets the discontinuous coverage maximum NAS signalling wait time value to a random value up to and including the stored discontinuous coverage maximum NAS signalling wait time for this PLMN and satellite NG-RAN RAT type, and starts this timer. The UE (102) shall not initiate any NAS signalling on that satellite NG-RAN RAT Type and PLMN while the discontinuous coverage maximum NAS signalling wait timer is running. The UE (102) shall stop the discontinuous coverage maximum NAS signalling wait timer and initiate NAS signalling if the UE (102) receives paging message, has pending emergency services, or when the UE (102) enters a TAI outside the registration area.

[0076] In an embodiment, when the unavailability period is activated, all NAS timers are stopped and associated procedures aborted except for timers T3512, T3346, T3447, T3396, T3584, T3585, any back-off timers, T3247, and the timer T controlling the periodic search for HPLMN or EHPLMN or higher prioritized PLMNs (see 3GPP TS 23.122 [5]).

[0077] In an embodiment, when the UE (102) activates the unavailability period using registration procedure, then after successful completion of the procedure, the UE (102) shall enter the state 5GMM-REGISTERED.NO-CELL-AVAILABLE.

[0078] In an embodiment, when the UE (102) activates the unavailability period using the de-registration procedure, then after successful completion of the procedure, the UE (102) shall enter the state 5GMM-DEREGISTERED.NO-CELL-AVAILABLE.

[0079] In an embodiment, the term EMM sublayer states are at least one of the below:

[0080] 1) EMM-NULL

[0081] 2) EMM-DEREGISTERED

[0082] a) EMM-DEREGISTERED.NORMAL-SERVICE

[0083] b) EMM-DEREGISTERED.LIMITED-SERVICE

[0084] c) EMM-DEREGISTERED.ATTEMPTING-TO-ATTACH

[0085] d) EMM-DEREGISTERED.PLMN-SEARCH

[0086] e) EMM-DEREGISTERED.NO-IMSI

[0087] f) EMM-DEREGISTERED.ATTACH-NEEDED

[0088] g) EMM-DEREGISTERED.NO-CELL-AVAILABLE

[0089] h) EMM-DEREGISTERED.eCALL-INACTIVE

[0090] 3) EMM-REGISTERED-INITIATED

[0091] 4) EMM-REGISTERED

[0092] a) EMM-REGISTERED.NORMAL-SERVICE

[0093] b) EMM-REGISTERED.ATTEMPTING-TO-UPDATE

[0094] c) EMM-REGISTERED.LIMITED-SERVICE

[0095] d) EMM-REGISTERED.PLMN-SEARCH

[0096] e) EMM-REGISTERED.UPDATE-NEEDED

[0097] f) EMM-REGISTERED.NO-CELL-AVAILABLE

[0098] g) EMM-REGISTERED.ATTEMPTING-TO-UPDATE-MM

[0099] h) EMM-REGISTERED.IMSI-DETACH-INITIATED

[0100] 5) EMM-DEREGISTERED-INITIATED

[0101] 6) EMM-TRACKING-AREA-UPDATING-INITIATED

[0102] 7) EMM-SERVICE-REQUEST-INITIATED

[0103] The term 5GMM sublayer state in this embodiment is at least one of the below:

[0104] 1) 5GMM-NULL

[0105] 2) 5GMM-DEREGISTERED

[0106] a) 5GMM-DEREGISTERED.NORMAL-SERVICE

[0107] b) 5GMM-DEREGISTERED.LIMITED-SERVICE

[0108] c) 5GMM-DEREGISTERED.ATTEMPTING-REGISTRATION

[0109] d) 5GMM-DEREGISTERED.PLMN-SEARCH

[0110] e) 5GMM-DEREGISTERED.NO-SUPI

[0111] f) 5GMM-DEREGISTERED.NO-CELL-AVAILABLE

[0112] g) 5GMM-DEREGISTERED.eCALL-INACTIVE

[0113] h) 5GMM-DEREGISTERED.INITIAL-REGISTRATION-NEEDED

[0114] 3) 5GMM-REGISTERED-INITIATED

[0115] 4) 5GMM-REGISTERED

[0116] a) 5GMM-REGISTERED.NORMAL-SERVICE

[0117] b) 5GMM-REGISTERED.NON-ALLOWED-SERVICE

[0118] c)5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE

[0119] d) 5GMM-REGISTERED.LIMITED-SERVICE

[0120] e) 5GMM-REGISTERED.PLMN-SEARCH

[0121] f) 5GMM-REGISTERED.NO-CELL-AVAILABLE

[0122] g) 5GMM-REGISTERED.UPDATE-NEEDED

[0123] 5) 5GMM-DEREGISTERED-INITIATED

[0124] 6) 5GMM-SERVICE-REQUEST-INITIATED

[0125] 5GMM-IDLE mode: In this specification, if the term is used standalone, the UE (102) in 5GMM-IDLE mode means the UE (102) can be either in 5GMM-IDLE mode over 3GPP access or in 5GMM-IDLE mode over non-3GPP access.

[0126] 5GMM-CONNECTED mode: In this specification, if the term is used standalone, the UE (102) in 5GMM-CONNECTED mode means the UE (102) can be either in 5GMM-CONNECTED mode over 3GPP access or in 5GMM-CONNECTED mode over non-3GPP access.

[0127] 5GMM-IDLE mode over 3GPP access: The UE (102) is in 5GMM-IDLE mode over 3GPP access when no N1 NAS signalling connection between the UE (102) and the AMF apparatus (104) over 3GPP access exists. The term 5GMM-IDLE mode over 3GPP access used in the present document corresponds to the term CM-IDLE state for 3GPP access used in 3GPP　TS　23.501　[8].

[0128] 5GMM-CONNECTED mode over 3GPP access: The UE (102) is in 5GMM-CONNECTED mode over 3GPP access when an N1 NAS signalling connection between the UE (102) and the AMF apparatus (104) over 3GPP access exists. The term 5GMM-CONNECTED mode over 3GPP access used in the present document corresponds to the term CM-CONNECTED state for 3GPP access used in 3GPP　TS　23.501　[8].

[0129] In an embodiment, for a 5G system with satellite access, the following requirements apply:

[0130] - The 5G system shall support service continuity between NR terrestrial access network and NR satellite access networks owned by the same operator or owned by 2 different operators having an agreement.

[0131] Table 1 depicts the T3412 and Implicit detach Timer.

[0132] Timer AtNameValueEMM StateTrigger ConditionStopping ConditionExplanationUET3412Default 54 min.NOTE　2NOTE　5EMM-REGISTEREDIn EMM-REGISTERED, when EMM-CONNECTED mode is left.When entering state EMM-DEREGISTERED or when entering EMM-CONNECTED mode.Initiation of the periodic TAU procedure　if the UE is not attached for emergency bearer services.Implicit detach from network if the UE is attached for emergency bearer services.NetworkMobile　reachableDefault 4 min greater than T3412All except EMM-DEREGISTEREDEntering EMM-IDLE modeNAS signalling connection establishedNetwork dependent, but typically paging is halted on 1st expiry　if the UE is not attached for emergency bearer services.Implicitly detach the UE which is attached for emergency bearer services.NetworkImplicit detach timerNOTE 3All except EMM-DEREGISTEREDThe mobile reachable timer expires while the network is in EMM-IDLE modeNAS signalling connection establishedImplicitly detach the UE　on 1st expiry

[0133] NOTE　2:　The value of this timer is provided by the network operator during　the attach　and tracking area updating procedures.

[0134] NOTE　3:　The value of this timer is　network dependent.　If ISR is activated, the　default　value of this timer is 4 minutes greater than T3423.

[0135] NOTE　5:　The default value of this timer is used if the network does not indicate a value in the TRACKING AREA UPDATE ACCEPT message and the UE (102) does not have a stored value for this timer.

[0136] Table 2 depicts the T3512 and Implicit De-registration Timer.

[0137] Timer AtNameValueEMM StateTrigger ConditionStopping ConditionExplanationUET3512Default 54minNOTE 15GMM-REGISTEREDIn 5GMM-REGISTERED, when5GMM-CONNECTED mode isleftWhen entering state5GMM-DEREGISTERED orwhen entering5GMM-CONNECTED modeInitiation of the periodic registration procedure if the UE is not registered for emergency services.Locally deregister if the UE is registered for emergency servicesAMFMobile reachable timerNOTE 1all except 5GMM-DEREGISTEREDEntering 5GMM-IDLE modeN1 NAS signalling connection establishedNetwork dependent, but typically paging is halted on 1st expiry, and start implicit de-registration timer, if the UE is not registered for emergency services. Implicitly de-register the UE which is registered for emergency servicesAMFimplicit de-registration timerNOTE 2all except 5GMM-DEREGISTEREDThe mobile reachable timer expires while the network is in 5GMM-IDLE modeN1 NAS signalling connection establishedImplicitly de-register the UE on 1st expiry

[0138] NOTE 1(UE): The value of this timer is provided by the network operator during the registration procedure.

[0139] NOTE 1(AMF): The default value of this timer is 4 minutes greater than T3512. If the UE (102) is registered for emergency services, the value of this timer is set equal to T3512.

[0140] If the T3346 value provided in the mobility management messages is greater than timer T3512, the AMF apparatus (104) sets the mobile reachable timer and the implicit de-registration timer such that the sum of the timer values is greater than timer T3346 value.

[0141] NOTE 2: The value of this timer is network dependent. If MICO is activated, the default value of this timer is 4 minutes greater than T3512.

[0142] In an embodiment, if the UE (102) and AMF apparatus (104) support unavailability period and an event is triggered in the UE (102) that would make it unavailable or lose coverage for a certain period of time, the UE (102) uses a Support of Unavailability Period to inform the AMF apparatus (104) of the upcoming unavailability and whether it is due to a NR satellite access discontinuous coverage. Use of the Support of Unavailability Period for loss of coverage due to the NR satellite access discontinuous coverage shall only be used if both UE (102) and the AMF apparatus (104) signalled "discontinuous coverage support".

[0143] During registration procedure for initial registration and each mobility registration update, the UE (102) supporting discontinuous coverage provides "Discontinuous Coverage Support" indication as part of UE MM Core Network Capability in the Registration Request message or in any AS / NAS signalling message to the AMF apparatus (104) or any Network Function / Entity. The AMF apparatus (104) receiving a Registration Request message from the UE (102) including "Discontinuous Coverage Support" indicates whether discontinuous coverage is supported by providing the "Discontinuous Coverage Support" indication to the UE (102) in the Registration Accept message or in any AS / NAS signalling message.

[0144] If the UE (102) and network support unavailability period and an event is triggered in the UE (102) making it unavailable for a certain period of time, the UE (102) may store its 5GMM and 5GSM context in USIM or non-volatile memory to be able to reuse it after the unavailability period.

[0145] The AMF apparatus (104) may take the Unavailability Period Duration (if available) and Start of Unavailability Period into account when determining the Periodic Registration Update timer value. The AMF apparatus (104) may provide a Periodic Registration Update time longer than or equal to the combination of the Unavailability Period Duration and Start of Unavailability Period to avoid interfering with the UE (102) dealing with the event that causes the unavailability.

[0146] During the registration procedure, the AMF apparatus (104) may determine the value of the periodic registration update timer (T3512) provided to the UE (102) based on the unavailability period duration (if available) and the start of the unavailability period.

[0147] The UE (102) and the AMF apparatus (104) re-negotiate unavailability at every Registration procedure, if it is required. If the Start of Unavailability Period and / or Unavailability Period Duration is not included in a Registration procedure any pending unavailability configuration stored in the UE (102), context at the AMF apparatus (104) is discarded.

[0148] In case the UE (102) requests power saving features, the AMF apparatus (104) provides the UE (102) with timers (e.g. Periodic Registration Update timer), extended DRX in CM-IDLE configuration, and MICO mode configuration, and to the NG-RAN Extended Connected Time. The AMF apparatus (104) may also consider the Unavailability Period Duration and Start of Unavailability Period (if available). This is to keep the UE (102) in power saving mode and avoid the network attempting to page the UE (102) if it is out of satellite network coverage.

[0149] The AMF apparatus (104) should adjust the mobile reachable timer or Implicit Deregistration timer or both such that the AMF apparatus (104) does not implicitly deregister the UE (102) while the UE (102) is unavailable.

[0150] The AMF apparatus (104) may determine the periodic update timer value based on the stored value of the Unavailability period duration IE, or based on a network determined unavailability period duration when the Unavailability period duration IE is not provided by the UE (102). If the UE (102) does not provide the Unavailability period duration IE in the REGISTRATION REQUEST message, the AMF apparatus (104) shall delete any stored value of the Unavailability period duration IE if exists.

[0151] 3GPP TS 23.501:

[0152] Clause 5.4.13 Support of discontinuous network coverage for satellite access:

[0153] 5.4.13.5 Overload control:

[0154] The AMF apparatus (104) and the UE (102) may only use the procedure defined in this clause if both the UE (102) and the AMF apparatus (104) indicate support for "Unavailability Period Support", see clause　5.4.13.1. The UE (102) indicating support for "Unavailability Period Support" shall support the procedures defined in this clause when leaving coverage and re-gaining coverage for an NR satellite RAT.

[0155] To avoid a large number of UEs causing excessive signalling load on the network when leaving coverage or re-gaining coverage after being out of coverage, the AMF apparatus (104) may determine a Maximum Time Offset controlling when the UEs are allowed to initiate NAS signalling with the network, as described in this clause.

[0156] The terms Maximum Time Offset, Maximum Waiting Time Offset, Discontinuous coverage Maximum time offset, discontinuous coverage wait timer, Discontinuous coverage maximum wait time, discontinuous coverage maximum NAS signalling wait time, discontinuous coverage maximum NAS signalling wait timer, Discontinuous coverage maximum NAS signalling wait time information and the Estimated Maximum Wait Time are all used interchangeably and have the same meaning.

[0157] In this case, the AMF apparatus (104) determines this Maximum Time Offset based on network configuration, priority users and priority service as specified in TS　23.122　and TS　24.501. The AMF apparatus (104) sends this Maximum Time Offset to individual UEs during the Registration procedure or UE Configuration Update procedure.

[0158] If the UE (102) receives a Maximum Time Offset from the network in a Registration Accept or UE Configuration Update Command message, the UE (102) shall replace any previously received Maximum Time Offset on the same RAT type and PLMN with this one.

[0159] When the UE (102) knows a later time at which coverage will be lost and when the UE (102) does not send a Mobility Registration Update to the AMF apparatus (104) in advance (see clause　5.4.13.1), the UE (102) determines a random value up to and including the latest Maximum Time Offset for this PLMN and RAT type. The UE (102) also determines an earlier time equal to the later time when coverage will be less than the random value. The UE (102) shall send the Mobility Registration Update at that earlier time to the AMF apparatus (104) indicating the loss of coverage.

[0160] Upon returning in coverage after being out of coverage due to discontinuous coverage, the UE (102) sets the discontinuous coverage wait timer value to a random value up to and including the latest Maximum Time Offset for this PLMN and RAT type, and starts this timer. The UE (102) shall not initiate any NAS signalling on that RAT Type and PLMN while the discontinuous coverage wait timer is running.

[0161] The UE (102) shall stop the discontinuous coverage wait timer and initiate NAS signalling if the UE (102) receives paging message, has pending emergency services, or when the UE (102) enters a TAI outside the registration area.

[0162] If the UE (102) is using an eNodeB that provides discontinuous coverage (e.g. for satellite access with discontinuous coverage), the UE (102) may indicate its Enhanced Discontinuous Coverage Support in the UE Core Network Capability in ATTACH Request message or TAU Request message or in any AS / NAS signalling message.

[0163] If the UE (102) has indicated Enhanced Discontinuous Coverage Support in UE Core Network Capability, the MME shall indicate to the UE (102) whether the corresponding feature is supported by providing the Enhanced Discontinuous Coverage Supported indication in the ATTACH Accept message or TAU Accept message or in any AS / NAS signalling message.

[0164] During Attach or TAU procedures, the UE (102) supporting Enhanced Discontinuous Coverage provides "Enhanced Discontinuous Coverage Support" indication as part of UE Core Network Capability in the Attach Request or TAU Request message to the MME. The MME receiving an Attach Request or a TAU Request message from the UE (102) including "Enhanced Discontinuous Coverage Support" indicates whether Enhanced Discontinuous Coverage is supported by providing the "Enhanced Discontinuous Coverage Support" indication to the UE (102) in the Attach Accept or TAU Accept message.

[0165] During Attach and TAU procedures the MME allocates the periodic RAU / TAU timer value as periodic TAU timer to the UE (102) based on VPLMN operator policy, low access priority indication from the UE (102), periodic RAU / TAU timer value requested by UE (102), subscription information received from the HSS and Start of Unavailability Period and / or Unavailability Period Duration, if using a RAN that provides discontinuous coverage.

[0166] The UE (102) and the MME re-negotiate unavailability at every TAU procedure, if it is required. If Start of Unavailability Period and / or Unavailability Period Duration is not included in a TAU Request message any pending loss of coverage configuration stored in the UE (102) context at MME is discarded.

[0167] If the UE (102) requests power saving features the MME provides the UE (102) with timers (e.g. periodic TAU timer, extended idle mode DRX, and PSM mode configuration, and may also consider the Unavailability Period Duration (if available) and Start of Unavailability Period (if available).

[0168] The MME should adjust the mobile reachable timer or Implicit Detach timer or both, such that the MME does not implicitly detach the UE (102) while the UE (102) is out of coverage

[0169] 3GPP TS 23.401:

[0170] Clause 4.13.8 Enhanced support of discontinuous network coverage for satellite access:

[0171] 4.13.8.6 Overload control:

[0172] The MME and UE (102) may only use the procedure defined in this clause if both the UE (102) and MME indicate "Enhanced Discontinuous Coverage Support".

[0173] In order to avoid a large number of UEs causing excessive signalling load on the network when leaving coverage or re-gaining coverage after being out of coverage, the MME may determine a Maximum Time Offset controlling when the UEs are allowed to initiate NAS signalling with the network, as described in this clause. In this case, the MME determines this Maximum Time Offset based on network configuration, priority users and priority services. The MME sends this maximum time offset to individual UEs during the Attach or TAU procedures. If the UE (102) receives this Maximum Time Offset from the network in an Attach or TAU Accept, the UE (102) shall replace any previously received Maximum Time Offset on the same RAT type and PLMN with this one.

[0174] When the UE (102) knows a later time at which coverage will be lost and when the UE (102) does not send a TAU Request to the MME in advance, the UE (102) determines a random value up to and including the latest Maximum Time Offset for this PLMN and RAT type and determines an earlier time equal to the later time when coverage will be lost less the random value. The UE (102) shall send the TAU Request at that earlier time to the MME indicating the loss of coverage.

[0175] Upon returning to coverage after being out of coverage due to discontinuous coverage, the UE (102) sets the discontinuous coverage wait timer value to a random value up to and including the latest Maximum Time Offset for this PLMN and RAT type, and starts this timer. The UE (102) shall not initiate any NAS signalling on that RAT Type and PLMN while the discontinuous coverage wait timer is running.

[0176] The UE (102) shall stop the discontinuous coverage wait timer and initiate NAS signalling if the UE (102) receives paging message, has pending emergency services, or when the UE (102) enters a Tracking Area outside the current Tracking Area List.

[0177] In the current art, the UE (102) may initiate the registration procedure when the AS layer (102B) is accessible and when it is still active. In this way, even while it is still mismatched and unable to handle it, the UE (102) would become available on the network side and be able to begin any network-initiated actions, such as information connections and paging. The UE (102) may also send NAS messages to the network while it is not in use. When the AS layer (102B) is kept active throughout the unavailability time, the UE (102) performs AS-related processes. This may this lead to high battery consumption and excess power usage.

[0178] In the proposed solution, the UE (102) is handled during an unavailability period in a wireless communication system. Here, the AS layer (102B) is deactivated when the unavailability period of the UE (102) is activated. This causes the AS layer (102B) to stop performing any AS layer related procedures. The UE (102) activates the AS layer (102B) only when it comes out of the unavailability period. Once the AS layer (102B) is activated, the UE (102) may initiate the registration procedure.

[0179] FIG. 3 is a scenario diagram that illustrates a scenario in which the UE (102) is de-registered / detached by a network apparatus (106) according to the prior art. For instance, the network apparatus (106) may also be referred to as the AMF apparatus (104), the mobility management entity (MME), a session management function (SMF), or any network function entity. Since the UE (102) is de-registered / detached by the network apparatus (106), the UE (102) cannot perform periodic registration update / mobility and periodic registration / TAU after at least one of the timer T3512, the periodic update timer, the periodic registration timer, and timer T3412 expires.

[0180] The network apparatus (106) provides the UE (102) with Periodic Registration Update timer (or Timer T3512), Periodic Update Timer, Periodic Registration Timer, or Periodic TAU timer (or Timer T3412) or an T3412 Extended Value or an extended T3412 timer for the UE (102) supporting discontinuous period or discontinuous coverage (for example, due to NR Satellite discontinuous coverage or E-UTRAN Satellite discontinuous coverage) based on the Start of Unavailability Period (if available) and Unavailability period (if available). The unavailability period details may be indicated / reported by the UE (102), determined by the network apparatus (106), or negotiated between the UE (102) and the network apparatus (106). The AMF apparatus (104) may take the Unavailability Period Duration (if available) and Start of Unavailability Period into account when determining the Periodic Registration Update timer value. The AMF apparatus (104) may provide a Periodic Registration Update time longer than or equal to the combination of the Unavailability Period Duration and Start of Unavailability Period to avoid interfering with the UE (102) dealing with the event that causes the unavailability.

[0181] During the registration procedure, the AMF apparatus (104) may determine the value of the periodic registration update timer (T3512) provided to the UE (102) based on the unavailability period duration (if available) and the start of the unavailability period. The AMF apparatus (104) may determine the periodic update timer value based on the stored value of the Unavailability period duration IE, or based on a network determined unavailability period duration when the Unavailability period duration IE is not provided by the UE (102). During Attach and TAU procedures, the MME allocates the periodic RAU / TAU timer value as periodic TAU timer to the UE (102) based on VPLMN operator policy, low access priority indication from the UE (102), periodic RAU / TAU timer value requested by UE (102), subscription information received from the HSS, and the Start of Unavailability Period and / or Unavailability Period Duration, if using a RAN that provides discontinuous coverage.

[0182] The network apparatus (106) also updates the Implicit de-registration timer / Implicit Detach timer and / or mobile reachable timer for the UE (102) based on the above information received from the UE (102) or determined by the network apparatus (106) itself. The AMF apparatus (104) should adjust the mobile reachable timer or Implicit Deregistration timer or both, such that the AMF apparatus (104) does not implicitly deregister the UE (102) while the UE (102) is unavailable. The MME should adjust the mobile reachable timer or Implicit Detach timer or both, such that the MME does not implicitly detach the UE (102) while the UE (102) is out of coverage. If the UE (102) requests power saving features, the AMF apparatus (104) provides the UE (102) with timers (e.g., Periodic Registration Update timer), extended DRX in CM-IDLE configuration, MICO mode configuration, an T3412 Extended Value or an extended T3412 timer, a plurality of negotiated extended DRX parameters, a plurality of extended idle mode DRX cycle parameters, an active Timer (T3324), a MICO mode (Mobile initiated connection only) configuration timer, an extended connected time, a plurality of Power saving mode (PSM) mode configuration parameters, a T3324 Extended Connected time timer and to the NG-RAN Extended Connected Time. The AMF apparatus (104) may also consider the Unavailability Period Duration (if available) and Start of Unavailability Period (if available). This is to keep the UE (102) in power saving mode and avoid the network apparatus (106) attempting to page the UE (102) if it is out of satellite network coverage. If the UE (102) requests power saving features, the MME provides the UE (102) with timers (e.g., periodic TAU timer, extended idle mode DRX, and PSM mode configuration, and may also consider the Unavailability Period Duration (if available) and Start of Unavailability Period (if available).

[0183] Power saving mechanisms / timers / parameters, being discussed in this embodiment, not restricted or limited to only these / below parameters / procedures / timers, are:

[0184] - Active Time / Active Timer / MICO mode with Active Time / MICO mode indication IE / T3324;

[0185] - Extended Connected Time / MICO mode with Extended Connected time;

[0186] - Periodic TAU Timer / Periodic Update Timer;

[0187] - Periodic Registration Timer / Periodic Registration Update Timer;

[0188] - eDRX parameters (such as cycle length i.e. DRX cycle parameter T) or extended idle mode DRX;

[0189] - PSM mode configuration; and

[0190] - PSM / MICO / eDRX.

[0191] Timers or parameters discussed in this embodiment are illustrated using few parameters / timers / values and may refer to (but not restricted to) any of the below timers or parameters or values :

[0192] the periodic tracking area update timer (T3412)

[0193] T3412 Extended Timer / Extended T3412 Timer

[0194] Mobile reachable Timer

[0195] Implicit detach timer

[0196] periodic registration update timer (T3512)

[0197] implicit de-registration timer

[0198] negotiated extended DRX parameters (such as cycle length i.e. DRX cycle parameter T) or

[0199] extended idle mode DRX cycle parameters

[0200] Active Timer (T3324)

[0201] MICO mode configuration

[0202] Extended Connected Time

[0203] PSM mode configuration parameters

[0204] Active Time / Active Timer / MICO mode with Active Time / MICO mode indication IE / T3324

[0205] Extended Connected Time / MICO mode with Extended Connected time

[0206] The network apparatus (106) for overload control also provides all the UEs with Maximum Waiting Time Offset / maximum time offset value. Upon returning to coverage after being out of coverage due to discontinuous coverage, the UE (102) sets the discontinuous coverage wait timer value to a random value up to and including the latest Maximum Time Offset for this PLMN and RAT type, and starts this timer. The UE (102) shall not initiate any NAS signaling on that RAT Type and PLMN while the discontinuous coverage wait timer is running. The terms Maximum Time Offset, Maximum Waiting Time Offset, Discontinuous coverage Maximum time offset, discontinuous coverage wait timer, Discontinuous coverage maximum wait time, discontinuous coverage maximum NAS signaling wait time, discontinuous coverage maximum NAS signaling wait timer, Discontinuous coverage maximum NAS signaling wait time information and the Estimated Maximum Wait Time are all used interchangeably and have the same meaning.

[0207] The UE (102) performs periodic registration update with the network apparatus (106) during any random value between 0 and Maximum time offset after it returns to coverage after the unavailability period ends. The network apparatus (106) only considers the unavailability period duration (if available) and / or the start of the unavailability period (if available), and does not consider or take into account the discontinuous coverage maximum NAS signalling wait time (or the Maximum Waiting Time offset or any name) while determining the values of any of the below parameters / procedure:

[0208] - the Periodic Registration Update timer (or Timer T3512) or Periodic Update Timer or Periodic Registration Timer or Periodic TAU timer (or Timer T3412) or the mobile reachable timer or Implicit Deregistration timer or Implicit Detach timer; and / or

[0209] - Power saving features / parameters / timers such as (but not restricted to) extended DRX in CM-IDLE configuration, MICO mode configuration, Extended Connected Time, extended idle mode DRX, PSM mode configuration, or other power saving parameters such as Active Time / Active Timer / MICO mode with Active Time / MICO mode indication IE / T3324, Extended Connected Time / MICO mode with Extended Connected time, eDRX parameters (such as cycle length, i.e., DRX cycle parameter T) or extended idle mode DRX, PSM / MICO / eDRX etc.

[0210] If the value / range of the Maximum Waiting Time Offset / maximum time offset or the discontinuous coverage maximum NAS signaling wait time or any such name or the random value chosen / determined by the UE (102) (up to and including the Maximum Waiting Time Offset / maximum time offset or the discontinuous coverage maximum NAS signaling wait time) for the discontinuous coverage wait timer value or the sum of the Maximum Waiting Time Offset / maximum time offset and unavailability period duration after the start of the unavailability period is high or large enough or more than the individual value or the value of the combination of any / all / combination of Periodic Registration Update timer (or Timer T3512) / Periodic TAU timer(or Timer T3412), the mobile reachable timer and / or or Implicit Deregistration timer or Implicit Detach timer, the UE (102) would be implicitly deregistered / detached while the UE (102) is unavailable or while the UE (102) is out of coverage.

[0211] If the Sum of Maximum time offset value and Unavailability Period duration after start of unavailability period is more than value(s) or the sum of at-least one or more or any or all of Periodic Registration Update timer (or Timer T3512) / Periodic TAU timer(or Timer T3412), the mobile reachable timer and / or implicit de-registration / detach timer for the UE (102), then the UE (102) might get implicitly de-registered / detached by the network apparatus (106) before the UE (102) can trigger Mobility and Periodic Registration update procedure or TAU procedure after coming out of discontinuous coverage.. This will cause the UE (102) to get de-registered / detached from the network apparatus (106). A method needs to be defined so that UE (102) is not de-registered in such a scenario.

[0212] For example, the Unavailability Period is 2 hours, and the network apparatus (106) has provided the maximum time offset as 10 min. The network apparatus (106) has the periodic registration update timer as 2 hours, optionally just before the UE (102) entering the unavailability period or discontinuous coverage, and the implicit de-registration timer as 5 min after periodic registration update timer expiry for the UE (102) (for example, 2 hours and 5 min). After coming out of the unavailability period or discontinuous coverage (for example, after 2 hours), the UE (102) tries to perform the periodic registration update in 10 min (Maximum time offset) after the unavailability period ends (for example, a total of 2 hours 10 min). The network apparatus (106) would have already implicitly deregistered / detached the UE (102) (at 2 hours 5 min) at implicit de-registration / detach timer expiry even before the UE (102) can perform periodic registration / TAU update.

[0213] In another embodiment, if the value / range of the Maximum Waiting Time Offset / maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name or the random value chosen / determined by the UE (102) (up to and including the Maximum Waiting Time Offset / maximum time offset or the discontinuous coverage maximum NAS signalling wait time) for the discontinuous coverage wait timer value or the sum of the Maximum Waiting Time Offset / maximum time offset and unavailability period duration after the start of the unavailability period is high or large enough or more than the individual value or the value of the combination of any / all / combination of Power saving features / parameters / timers such as (but not restricted to) extended DRX in CM-IDLE configuration, MICO mode configuration, Extended Connected Time, extended idle mode DRX, PSM mode configuration, or other power saving parameters such as Active Time / Active Timer / MICO mode with Active Time / MICO mode indication IE / T3324, Extended Connected Time / MICO mode with Extended Connected time, eDRX parameters (such as cycle length i.e., DRX cycle parameter T) or extended idle mode DRX, PSM / MICO / eDRX. Then the network apparatus (106) might attempt to page the UE (102) even if the UE (102) is out of satellite network coverage or if the UE (102) is waiting for the discontinuous coverage wait timer / Maximum Waiting Time Offset / maximum time offset, or the discontinuous coverage maximum NAS signalling wait time to expire. A method needs to be defined to handle this situation.

[0214] TS 23.501 Sec 5.19.7 NAS level congestion control:

[0215] NAS level congestion control is achieved by providing the UE (102) a back-off time. To avoid that large amounts of UEs initiate deferred requests (almost) simultaneously, the 5GC should select each back-off time value so that the deferred requests are not synchronized. When the UE (102) receives a back-off time, the UE (102) shall not initiate any NAS signalling with regards to the applied congestion control until the back-off timer expires or the UE (102) receives a mobile terminated request from the network apparatus (106), or the UE (102) initiates signalling for emergency services or high priority access. The network apparatus (106) may apply NAS level congestion control, but should not apply NAS level congestion control for procedures not subject to congestion control. While the Mobility Management back-off timer is running, the UE (102) shall not initiate any NAS request except for Deregistration procedure and procedures not subject to congestion control (e.g., high priority access, emergency services) and mobile terminated services. After any such Deregistration procedure, the back-off timer continues to run.

[0216] When the NAS MM congestion control is activated at the AMF apparatus (104) and if the UE (102) indicates that the NAS MM message is exempted from NAS congestion control, the AMF apparatus (104) shall not reject the NAS MM message and shall forward the NAS SM message to the corresponding SMF with an indication that the NAS SM message was indicated to be exempted from NAS congestion control. If the AMF apparatus (104) rejects Registration Request messages or Service Request with a Mobility Management back-off time which is larger than the sum of the UE's Periodic Registration Update timer and the Implicit Deregistration timer, the AMF apparatus (104) should adjust the mobile reachable timer and / or Implicit Deregistration timer such that the AMF apparatus (104) does not implicitly deregister the UE (102) while the Mobility Management back-off timer is running.

[0217] TS 24.501 Sec 5.3.9 Handling of NAS level mobility management congestion control:

[0218] The AMF apparatus (104) may detect 5GMM signalling congestion and perform general NAS level congestion control. Under the 5GMM signalling congestion conditions the AMF apparatus (104) may reject 5GMM signalling requests from the UE (102). The AMF apparatus (104) should not reject requests for emergency services, requests for emergency services fall back, requests from the UE (102) configured for high priority access in selected PLMN or SNPN, DEREGISTRATION REQUEST message, requests for mobile terminated services triggered by paging or a notification procedure, and requests for initial registration or mobility and periodic registration update when emergency is indicated by lower layers.

[0219] When general NAS level congestion control is active, the AMF apparatus (104) may include a value for the mobility management back-off timer T3346 in the reject messages. The UE (102) starts the timer T3346 with the value received in the 5GMM reject messages. To avoid that large numbers of UEs simultaneously initiating deferred requests, the AMF apparatus (104) should select the value for the timer T3346 for the rejected UEs so that timeouts are not synchronised. If the UE (102) is registered in the same PLMN over the 3GPP access and non-3GPP access, and the UE (102) receives the timer T3346 from the AMF apparatus (104), the timer T3346 shall apply to both 3GPP access and non-3GPP access. If the initial registration request is rejected due to general NAS level mobility management congestion control, the network apparatus (106) shall set the 5GMM cause value to #22 "congestion" and assign a value for back-off timer T3346. If the mobility and periodic registration update request is rejected due to general NAS level mobility management congestion control, the network shall set the 5GMM cause value to #22 "congestion" and assign a value for back-off timer T3346.

[0220] The AMF apparatus (104) may detect 5GMM signaling congestion and perform general NAS level congestion control. Under the 5GMM signaling congestion conditions, the AMF apparatus (104) may reject 5GMM signaling requests (for example, Registration Request messages or Service Request messages) from the UE (102) with a Mobility Management Back-off Timer (for example, Timer T3346). While the Mobility Management back-off timer is running, the UE (102) shall not initiate any NAS request except for Deregistration procedure and procedures not subject to congestion control (e.g., high priority access, emergency services) and mobile terminated services.

[0221] While the Mobility Management Back-off Timer (MM BO Timer) (for example, Timer T3346) is running, the UE (102) may lose coverage due to discontinuous coverage or the UE (102) may enter the discontinuous coverage. After the Mobility Management Back-off Timer ends, the UE (102) may initiate any NAS signaling towards the network apparatus (106). However, since the UE (102) has already entered discontinuous coverage, the UE (102) may not be able to initiate any AS / NAS signaling towards the network apparatus (106). If the Periodic Registration Update timer of the UE (102) or the Implicit Deregistration timer or the sum of the Periodic Registration Update timer and the Implicit Deregistration timer expires, the network apparatus (106) may implicitly deregister / detach the UE (102) optionally since the UE (102) didn't indicate / negotiate to the network apparatus (106) that the UE (102) is about to enter / is entering / is in discontinuous coverage.

[0222] In an embodiment, there may be a situation where the MM Back-off Timer expires and the UE (102) might be in the unavailability period (for example, the UE (102) unavailability period might be larger than the set or received back-off timer by the UE (102). In such situations, the network apparatus (106) would not come to know that the UE (102) is in the unavailability period and the network apparatus (106) might deregister or detach the UE (102). This is not a correct behaviour as the network apparatus (106) shall not deregister / detach the UE (102) while the UE (102) is in discontinuous coverage.

[0223] For example, the UE (102) gets a Mobility Management Back-off Timer (for example, Timer T3346) from the network apparatus (106) at 10am with a Timer value of 1 hour. The Implicit Deregistration timer may be set to a value of 1.5 hours. The UE (102) runs the Mobility Management Back-off Timer from 10AM to 11AM (of duration 1hour). At 10.30AM, the UE (102) may enter discontinuous coverage for 2 hours duration (10.30AM-12.30PM) (for example, the UE (102) has a long unavailability period). The unavailability period might be a large value or the unavailability period is more than the value or the sum of the values of the Back-off timer and / or implicit deregistration / detach timer / mobile reachable timer / periodic timer. The network apparatus (106) may run an Implicit Deregistration / Detach timer from the UE (102) from 10am with a duration of 1.5 hours (10AM-11.30AM). Since the UE (102) entered the discontinuous coverage and the network apparatus (106) is not aware that the UE (102) has entered discontinuous coverage, the network apparatus (106) may implicitly deregister / detach the UE (102).

[0224] Referring now to the drawings, and more particularly to FIGS. 4 through 11 where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.

[0225] 3 GPP: Third Generation Partnership Project

[0226] 4G-GUTI: 4G-Globally Unique Temporary Identifier

[0227] 5G-BRG: 5G Broadband Residential Gateway

[0228] 5GC: 5G Core

[0229] 5GCN: 5G Core Network

[0230] 5G-CRG: 5G Cable Residential Gateway

[0231] 5G-GUTI: 5G-Globally Unique Temporary Identifier

[0232] 5GMM: 5G Mobility Management

[0233] 5G-RG : 5G Residential Gateway

[0234] 5GS: 5G System

[0235] 5GSM: 5GS Session Management

[0236] 5G-S-TMSI: 5G S-Temporary Mobile Subscription Identifier

[0237] 5G-TMSI: 5G Temporary Mobile Subscription Identifier

[0238] 5QI: 5G QoS Identifier

[0239] ACS: Auto-Configuration Server

[0240] AKA: Authentication and Key Agreement

[0241] A-KID: AKMA Key Identifier

[0242] AKMA: Authentication and Key Management for Applications

[0243] AMBR: Aggregate Maximum Bit Rate

[0244] AMF: Access and Mobility Management Function

[0245] APN: Access Point Name

[0246] ARP: Allocation and Retention Policy

[0247] AS: Access Stratum

[0248] A-TID: AKMA Temporary Identifier

[0249] ATSSS: Access Traffic Steering, Switching and Splitting

[0250] AUSF: Authentication Server Function

[0251] CAG: Closed access group

[0252] CAG ID: Closed Access Group Identifier

[0253] CHAP: Challenge Handshake Authentication Protocol

[0254] CU: Centralized Unit

[0255] DC: Discontinuous Coverage

[0256] DisCo: Discontinuous Coverage

[0257] DL: Downlink

[0258] DND: Do not Disturb

[0259] DRX: Discontinuous Reception

[0260] DU: Distributed Unit

[0261] eDRX: Extended Discontinuous Reception

[0262] EHPLMN: Equivalent Home Public Land Mobile Network

[0263] EMM: EUTRA Mobility Management

[0264] eNB: Evolved Node-B

[0265] eNPN: Enhanced Non-Public Networks

[0266] EPC: Evolved Packet Core

[0267] EPLMN: Equivalent Public Land Mobile Network

[0268] EPS: Evolved Packet System

[0269] eSIM: embedded Subscriber Identity Module

[0270] E-UTRA: Evolved Universal Mobile Telecommunication Access

[0271] EUTRAN: Evolved Universal Mobile Telecommunication Access Network

[0272] FPLMN: Forbidden Public Land Mobile Network

[0273] FR: Frequency Range

[0274] GEO: Geostationary Orbit

[0275] GERAN: GSM Edge Radio Access Network

[0276] GERAN EC-GSM-IoT: GSM Edge Radio Access Network Extended Coverage -GSM-Internet of Things

[0277] gNB: Next generation Node-B

[0278] gNB - CU: Next generation Node-B Control Unit

[0279] gNB - DU: Next generation Node-B Distributive Unit

[0280] GPRS: General Packet Radio Service

[0281] GPS: Global Positioning System

[0282] GSM: Global System for Mobile Communication

[0283] HPLMN: Home Public Land Mobile Network

[0284] IAB: Integrated access and backhaul

[0285] IAB-UE: The part of the IAB node that supports the Uu interface towards the IAB-donor or another parent IAB-node (and thus manages the backhaul connectivity with either PLMN or SNPN it is registered with) is referred to as an IAB-UE.

[0286] LADN: Local Area Data Network

[0287] LCS: Location services

[0288] LEO: Low Earth Orbit

[0289] MBSR: Mobile Base Station Relay

[0290] MCC: Mobile Country Code

[0291] MCS: Mission Critical Service

[0292] ME: Mobile Equipment

[0293] MEC: Multi-Access Edge Computing

[0294] MEO: Medium Earth Orbit

[0295] MICO: Mobile Initiated Communication Only

[0296] MINT: Minimization of service interruption

[0297] MME: Mobility Management Entity

[0298] MNC: Mobile Network Code

[0299] MPS: Multimedia Priority Service

[0300] MS: Mobile Station. The present document makes no distinction between MS and UE.

[0301] NAS: Non-Access Stratum

[0302] NB-S1 Mode: Narrow Band with S1 Interface

[0303] NGAP: Next Generation Application Protocol

[0304] NG-RAN: Next Generation Radio Access Network

[0305] NPN: Non-Public Networks

[0306] NR: New Radio

[0307] NTN: Non Terrestrial Networks

[0308] NW: Network

[0309] OOS: Out of Service

[0310] OS Upgrade: Operating System Upgrade

[0311] PDN: Packet Data Network

[0312] PDU: Packet Data Unit

[0313] PLMN ID: Public Land Mobile Network Identity

[0314] PSM: Power Saving Mode

[0315] QoS: Quality Of Service

[0316] RAT: Radio Access Technology

[0317] RPLMN: Registered Public Land Mobile Network

[0318] RRC: Radio Resource Control

[0319] RU: Registration Update

[0320] SAT: Satellite

[0321] Satellite: An artificial body placed in orbit round the earth or moon or another planet in order to collect information or for communication.

[0322] Satellite Constellation: Group of satellites, placed in orbit round the earth or moon or another planet in order to collect information or for communication.

[0323] Service User An individual who has received a priority level assignment from a regional / national authority (i.e., an agency authorised to issue priority assignments) and has a subscription to a mobile network operator.

[0324] SIM: Subscriber Identity Module

[0325] SNPN: Standalone Non-Public Networks

[0326] SUCI: Subscription Concealed Identifier

[0327] SW: Software

[0328] TAC: Tracking Area Code

[0329] TAI: Tracking Area Identity

[0330] TAU: Tracking Area Update

[0331] TER: Terrestrial

[0332] TN: Terrestrial Networks

[0333] UCU: UE Configuration Update

[0334] UDM: Unified Data Management Function

[0335] UE: User Equipment

[0336] UL: Uplink

[0337] ULI: User Location Information

[0338] UPU: UE Parameters Update

[0339] USIM: Universal Subscriber Identification Module

[0340] Uu: The radio interface between the UE (102) and the Node B

[0341] VMR: Vehicle Mounted Relay

[0342] VPLMN: Visited Public Land Mobile Network

[0343] WB-S1 Mode: Wide Band with S1 Interface

[0344] Visited PLMN (VPLMN): This is a PLMN different from the HPLMN (if the EHPLMN list is not present or is empty) or different from an EHPLMN (if the EHPLMN list is present).

[0345] Allowable PLMN: In the case of an MS operating in MS operation mode A or B, this is a PLMN which is not in the list of "forbidden PLMNs" in the MS. In the case of an MS operating in MS operation mode C or an MS not supporting A / Gb mode and not supporting Iu mode, this is a PLMN which is not in the list of "forbidden PLMNs" and not in the list of "forbidden PLMNs for GPRS service" in the MS.

[0346] Available PLMN: PLMN(s) in the given area which is / are broadcasting capability to provide wireless communication services to the UE.

[0347] Camped on a cell: The MS (ME if there is no SIM) has completed the cell selection / reselection process and has chosen a cell from which it plans to receive all available services. Note that the services may be limited, and that the PLMN or the SNPN may not be aware of the existence of the MS (ME) within the chosen cell.

[0348] EHPLMN: Any of the PLMN entries contained in the Equivalent HPLMN list.

[0349] Equivalent HPLMN list: To allow provision for multiple HPLMN codes, PLMN codes that are present within this list shall replace the HPLMN code derived from the IMSI for PLMN selection purposes. This list is stored on the USIM and is known as the EHPLMN list. The EHPLMN list may also contain the HPLMN code derived from the IMSI. If the HPLMN code derived from the IMSI is not present in the EHPLMN list, then it shall be treated as a Visited PLMN for PLMN selection purposes.

[0350] Home PLMN: This is a PLMN where the MCC and MNC of the PLMN identity match the MCC and MNC of the IMSI.

[0351] Registered PLMN (RPLMN): This is the PLMN on which certain LR (location registration which is also called as registration procedure) outcomes have occurred. In a shared network the RPLMN is the PLMN defined by the PLMN identity of the CN operator that has accepted the LR.

[0352] Registration: This is the process of camping on a cell of the PLMN or the SNPN and doing any necessary LRs.

[0353] UPLMN: PLMN / access technology combination in the "User Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order).

[0354] OPLMN: PLMN / access technology combination in the "Operator Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order) or stored in the ME (in priority order).

[0355] Examples of NAS messages can be, but not limited to, REGISTRATION REQUEST message; DEREGISTRATION REQUEST message; SERVICE REQUEST message; CONTROL PLANE SERVICE REQUEST; IDENTITY REQUEST; AUTHENTICATION REQUEST; AUTHENTICATION RESULT; AUTHENTICATION REJECT; REGISTRATION REJECT; REGISTRATION ACCEPT; DEREGISTRATION ACCEPT; SERVICE REJECT; SERVICE ACCEPT; UE CONFIGURATION UPDATE command; UE PARAMETERS UPDATE command, and so on.

[0356] The term 5GMM sublayer states in this embodiment are at least one of the below:

[0357] 1) 5GMM-NULL

[0358] 2) 5GMM-DEREGISTERED

[0359] a) 5GMM-DEREGISTERED.NORMAL-SERVICE

[0360] b) 5GMM-DEREGISTERED.LIMITED-SERVICE

[0361] c) 5GMM-DEREGISTERED.ATTEMPTING-REGISTRATION

[0362] d) 5GMM-DEREGISTERED.PLMN-SEARCH

[0363] e) 5GMM-DEREGISTERED.NO-SUPI

[0364] f) 5GMM-DEREGISTERED.NO-CELL-AVAILABLE

[0365] g) 5GMM-DEREGISTERED.eCALL-INACTIVE

[0366] h) 5GMM-DEREGISTERED.INITIAL-REGISTRATION-NEEDED

[0367] 3) 5GMM-REGISTERED-INITIATED

[0368] 4) 5GMM-REGISTERED

[0369] a) 5GMM-REGISTERED.NORMAL-SERVICE

[0370] b) 5GMM-REGISTERED.NON-ALLOWED-SERVICE

[0371] c) 5GMM-REGISTERED.ATTEMPTING-REGISTRATION-UPDATE

[0372] d) 5GMM-REGISTERED.LIMITED-SERVICE

[0373] e) 5GMM-REGISTERED.PLMN-SEARCH

[0374] f) 5GMM-REGISTERED.NO-CELL-AVAILABLE

[0375] g) 5GMM-REGISTERED.UPDATE-NEEDED

[0376] 5) 5GMM-DEREGISTERED-INITIATED

[0377] 6) 5GMM-SERVICE-REQUEST-INITIATED

[0378] In this embodiment, the term EMM sublayer states are at least one of the below:

[0379] 1) EMM-NULL

[0380] 2) EMM-DEREGISTERED

[0381] a) EMM-DEREGISTERED.NORMAL-SERVICE

[0382] b) EMM-DEREGISTERED.LIMITED-SERVICE

[0383] c) EMM-DEREGISTERED.ATTEMPTING-TO-ATTACH

[0384] d) EMM-DEREGISTERED.PLMN-SEARCH

[0385] e) EMM-DEREGISTERED.NO-IMSI

[0386] f) EMM-DEREGISTERED.ATTACH-NEEDED

[0387] g) EMM-DEREGISTERED.NO-CELL-AVAILABLE

[0388] h) EMM-DEREGISTERED.eCALL-INACTIVE

[0389] 3) EMM-REGISTERED-INITIATED

[0390] 4) EMM-REGISTERED

[0391] a) EMM-REGISTERED.NORMAL-SERVICE

[0392] b) EMM-REGISTERED.ATTEMPTING-TO-UPDATE

[0393] c) EMM-REGISTERED.LIMITED-SERVICE

[0394] d) EMM-REGISTERED.PLMN-SEARCH

[0395] e) EMM-REGISTERED.UPDATE-NEEDED

[0396] f) EMM-REGISTERED.NO-CELL-AVAILABLE

[0397] g) EMM-REGISTERED.ATTEMPTING-TO-UPDATE-MM

[0398] h) EMM-REGISTERED.IMSI-DETACH-INITIATED

[0399] 5) EMM-DEREGISTERED-INITIATED

[0400] 6) EMM-TRACKING-AREA-UPDATING-INITIATED

[0401] 7) EMM-SERVICE-REQUEST-INITIATED

[0402] The term RAT as defined in this embodiment can be one of the following: NG-RAN, 5G, 4G, 3G, 2G, EPS, 5GS, NR, NR in unlicensed bands, NR(LEO) satellite access, NR(MEO) satellite access, NR(GEO) satellite access, NR(OTHERSAT) satellite access, NR RedCap, E-UTRA, E-UTRA in unlicensed bands, NB-IoT, WB-IoT, LTE-M, and so on.

[0403] 5GS registration type may be initial registration, mobility registration updating, periodic registration updating, emergency registration, SNPN onboarding registration, disaster roaming initial registration, disaster roaming mobility registration updating, not set the registration type to disaster roaming initial registration or disaster roaming mobility registration updating means 5GS registration type is set to value other than "disaster roaming initial registration" or "disaster roaming mobility registration updating" at least one of: initial registration, mobility registration updating, periodic registration updating, emergency registration, SNPN onboarding registration, and so on), and so on.

[0404] PLMN selection as per 23.122 without RPLMN:

[0405] The MS selects and attempts registration on any PLMN / access technology combinations, if available and allowable, in the following order:

[0406] - Either the HPLMN (if the EHPLMN list is not present or is empty) or the highest priority EHPLMN that is available (if the EHPLMN list is present);

[0407] - Each PLMN / access technology combination in the "User Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order);

[0408] - Each PLMN / access technology combination in the "Operator Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order) or stored in the ME (in priority order);

[0409] - Other PLMN / access technology combinations with received high quality signal in random order; and

[0410] - Other PLMN / access technology combinations in order of decreasing signal quality.

[0411] PLMN selection as per 23.122 with RPLMN:

[0412] The MS selects and attempts registration on any PLMN / access technology combinations, if available and allowable, in the following order:

[0413] - Either the RPLMN or the Last registered PLMN;

[0414] - Either the HPLMN (if the EHPLMN list is not present or is empty) or the highest priority EHPLMN that is available (if the EHPLMN list is present);

[0415] - Each PLMN / access technology combination in the "User Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order);

[0416] - Each PLMN / access technology combination in the "Operator Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order) or stored in the ME (in priority order);

[0417] - Other PLMN / access technology combinations with received high quality signal in random order; and

[0418] - Other PLMN / access technology combinations in order of decreasing signal quality.

[0419] The terms UE (102) and MS are used interchangeably in this embodiment and have the same meaning.

[0420] The term area / location / geographical area are used in this embodiment may refer to any of cell / cell ID, TAC / TAI, PLMN ,MCC / MNC, Latitude / longitude, CAG cell or any geographical location / coordinate.

[0421] The solutions explained in this embodiment are applicable to any (but not limited to) of the RAT(s) as defined in this embodiment.

[0422] The network apparatus (106) used in this embodiment could be any 5G / EUTRAN Core Network Entities like AMF apparatus (104) / SMF / MME / UPF or the network apparatus (106) could be any (but not limited to) 5G / EUTRAN RAN Entity like eNodeB (eNB) or gNodeB (gNB) or NG-RAN etc.

[0423] The terms Maximum Time Offset, Maximum Waiting Time offset, Maximum wait time offset, Discontinuous coverage maximum wait time are used interchangeably and have same meaning.

[0424] Few of the power saving mechanisms / timers / parameters, being discussed in this embodiment, but not restricted or limited to only these, are:

[0425] - Active Time / Active Timer / MICO mode with Active Time / MICO mode indication IE / T3324;

[0426] - Extended Connected Time / MICO mode with Extended Connected time;

[0427] - Periodic TAU Timer / Periodic Update Timer;

[0428] - Periodic Registration Timer / Periodic Registration Update Timer;

[0429] - eDRX parameters (such as cycle length i.e. DRX cycle parameter T) or extended idle mode DRX;

[0430] - PSM mode configuration; and

[0431] - PSM / MICO / eDRX.

[0432] The NTN and TN could either operate in two different frequency bands (e.g. FR1 vs FR2), or in same frequency band (e.g. FR1 or FR2). The terms Satellite 3GPP access, Satellite access, Satellite Access Network, NR Satellite Access Network, Satellite NG-RAN Access Technology and NR Satellite access have been interchangeably used and have the same meaning.

[0433] The methods, issues or solutions disclosed in this embodiment are explained using NR satellite access or Satellite NG-RAN Access Technology as an example and is not restricted or limited to NR Satellite access only. However, the solutions proposed in this embodiment are also applicable for Satellite E-UTRAN access Technology, NB (Narrow Band)-S1 mode or WB(Wide Band)-S1 mode via satellite E-UTRAN access and / or NB-IOT (Narrowband Internet Of Things) or WB-IOT (Wideband Internet Of Things) Satellite Access / Architecture.

[0434] The solutions which are defined for NR (5GC) are also applicable to legacy RATs like E-UTRA / LTE, the corresponding CN entities needs to be replaced by LTE entities for e.g. AMF apparatus (104) with MME, g-nodeB with e-nodeB, UDM with HSS etc. But principles of the solution remains same.

[0435] An example list of NAS messages may include, but not limited to, REGISTRATION REQUEST message; DEREGISTRATION REQUEST message; SERVICE REQUEST message; CONTROL PLANE SERVICE REQUEST; IDENTITY REQUEST; AUTHENTICATION REQUEST; AUTHENTICATION RESULT; AUTHENTICATION REJECT; REGISTRATION REJECT; DEREGISTRATION ACCEPT; SERVICE REJECT; SERVICE ACCEPT, and the like.

[0436] The network apparatus (106) used in this embodiment is explained using any 5G Core Network Function for e.g. AMF apparatus (104). However, the network apparatus (106) could be any 5G / EUTRAN Core Network Entities like AMF apparatus (104) / SMF / MME / UPF or the Network could be any 5G / EUTRAN RAN Entity like eNodeB (eNB) or gNodeB (gNB) or NG-RAN etc.

[0437] The messages used or indicated in this embodiment are shown as an example. The messages could be any signalling messages between the UE (102) and the network apparatus (106).

[0438] The term area / location / geographical area are used in this embodiment may refer to any of cell / cell ID, TAC / TAI, PLMN ,MCC / MNC, Latitude / longitude, CAG cell or any geographical location / coordinate.

[0439] The methods, issues or solutions disclosed in this embodiment are explained using NR access or NG-RAN Access Technology as an example and is not restricted or limited to NR access only. However, the solutions proposed in this embodiment are also applicable for E-UTRAN access Technology, NB (Narrow Band)-S1 mode or WB (Wide Band)-S1 mode via E-UTRAN access and / or NB-IOT (Narrowband Internet of Things) or WB-IOT (Wideband Internet of Things) Access / Architecture.

[0440] The solutions which are defined for NR (5GC) are alo applicable to legacy RATs like E-UTRA / LTE, the corresponding CN entities needs to be replaced by LTE entities for e.g. AMF apparatus (104) with MME, g-nodeB with e-nodeB, UDM with HSS etc. But principles of the solution remains same.

[0441] The network apparatus (106) used in this embodiment is explained using any 5G Core Network Function for e.g. AMF apparatus (104). However, the network apparatus (106) could be any 5G / EUTRAN Core Network Entities like AMF apparatus (104) / SMF / MME / UPF or the Network could be any 5G / EUTRAN RAN Entity like eNodeB (eNB) or gNodeB (gNB) or NG-RAN etc.

[0442] The messages used or indicated in this embodiment are shown as an example. The messages could be any signalling messages between the UE (102) and the network apparatus (106).

[0443] The terms camp and register are used interchangeably and have the same meaning.

[0444] The terms wait timer, DisCo wait timer, Discontinuous Coverage wait timer, Random timer, Random wait timer, DCW Timer are all used interchangeably and have the same meaning.

[0445] The terms wait range, Disco Wait Range, Discontinuous Coverage Wait Range, and DCW Range are all used interchangeably and have the same meaning.

[0446] The term area as used in this embodiment may refer to any of cell / cell ID, TAC / TAI, PLMN ,MCC / MNC, Latitude / longitude, any CAG / CAG identifier or any geographical location / coordinate.

[0447] For the list of possible NAS messages please refer to 3GPP TS 24.501 or 3GPP TS 24.301, for list of AS messages please refer to 3GPP TS 38.331 or 3GPP TS 36.331

[0448] The cause names in this embodiment are for illustration purpose and it can have any name. The non-access stratum (NAS) messages and access stratum (AS) messages described in this embodiment is only for illustration purpose it can be any NAS or AS messages as per defined protocol between the UE (102) and AMF apparatus (104) / MME or the UE (102) and gNB (NG-RAN / any RAN node) / eNB.

[0449] The terms Maximum Time Offset, Maximum Waiting Time Offset, Discontinuous coverage Maximum time offset, discontinuous coverage wait timer, Discontinuous coverage maximum wait time, discontinuous coverage maximum NAS signalling wait time, discontinuous coverage maximum NAS signalling wait timer, Discontinuous coverage maximum NAS signalling wait time information and the Estimated Maximum Wait Time are all used interchangeably and have the same meaning.

[0450] The terms Enhanced Discontinuous Coverage, Enhanced Discontinuous Coverage, discontinuous coverage supported and discontinuous coverage support are all used interchangeably and have the same meaning.

[0451] The terms type of unavailability and unavailability type are all used interchangeably and have the same meaning.

[0452] The terms Unavailability Period Support, Support of Unavailability Period and Unavailability Period Supported are all used interchangeably and have the same meaning.

[0453] In this embodiment, the terms discontinuous coverage period and entering discontinuous coverage indication have same meaning and are used interchangeably. These indications are provided by the UE (102) to the network apparatus (106), when the UE (102) is about to enter discontinuous coverage.

[0454] In this embodiment, the terms discontinuous coverage, unavailability period, unavailability information and enhanced discontinuous coverage are used interchangeably and have the same meaning.

[0455] FIG. 4 is a block diagram that illustrates a schematic of the UE (102) implemented to carry out the disclosed subject matter, according to the embodiment as disclosed herein. As shown, the UE (102) includes a processor (402), a memory (404), an I / O interface (406), and a controller (408). The UE (102) may include, but not limited to a smartphone, personal computer (PC), tablet, and the like.

[0456] The processor (402) communicates with the memory (404), the I / O interface (406) and the controller (408). The processor (402) is configured to execute instructions stored in the memory (404) and to perform various processes. The processor (402) may include one or a plurality of processors, may be a general-purpose processor, such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an Artificial intelligence (AI) dedicated processor such as a neural processing unit (NPU).

[0457] The memory (404) includes storage locations to be addressable through the processor (402). The memory (404) is not limited to a volatile memory and / or a non-volatile memory. Further, the memory (404) may include a plurality of computer-readable storage media. The memory (404) may include non-volatile storage elements. For example, non-volatile storage elements may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories.

[0458] The I / O interface (406) transmits the information between the memory (404) and external peripheral devices. The peripheral devices are the input-output devices associated with the UE (102). Further, the controller (408) communicates with the I / O interface (406) and the memory (404). The controller (408) may be communicatively coupled to the memory (404) and the processor (402). The controller (408) is an innovative hardware that is realized through the physical implementation of both analog and digital circuits, including logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive and active electronic components, as well as optical components.

[0459] In an embodiment, the controller (408) detects whether the unavailability period has been activated by the UE (102) through a registration procedure between the UE (102) and the AMF apparatus (104). The time duration that the　UE (102)　is unavailable to access network services is referred to as its unavailability period duration. For example,　factors　like upgrades in the UE (102), might cause the UE (102) to enter an unavailability period. The AMF apparatus (104)　receives a registration request or a deregistration request from the UE (102) when it initiates an unavailability period, specifying the unavailability period duration.

[0460] The AMF apparatus (104) managing user access and mobility across the network. The AMF apparatus (104) manages the signaling between the UE (102) and the network, including the setup, modification, and release of connections (connection management). It also handles mobility events, such as handovers when the UE (102) moves from one cell to another (mobility management). The AMF function also include registration management and reachability management.

[0461] In an embodiment, the controller (408) deactivates the AS layer (102B) of the UE (102) when the UE (102) is currently in the unavailability period. The AS layer (102B) of the UE (102) is responsible for the radio communication between the UE (102) and a radio access network (RAN). The AS layer (102B) deals with all aspects of the radio interface, including the transmission, reception, and radio resource management. The AS layer (102B) is responsible for setting up, maintaining, and releasing radio bearers, which are the channels that carry user data and control messages over the air interface. Deactivation of the AS layer (102B) prevents the AS layer (102B) in performing the above mentioned functions during the unavailability period of the UE (102). Thus, excess battery or power consumption of the UE (102) during the unavailability period is avoided.

[0462] In an embodiment, the controller (408) determines whether the UE (102) has come out of the unavailability period. The controller (308) then activates the AS layer (102B) when the UE (102) come out of the unavailability period. The UE (102) comes out of the unavailability period only when the AS layer (102B) is deactivated.

[0463] In an embodiment, the controller (408) transmits a registration request message to the AMF apparatus (104) for initiating the registration procedure upon activation of the AS layer (102B). For example, the registration request message may include an identity of the UE (102), security capabilities of the UE (102), and other necessary information associated with the UE (102).

[0464] In an embodiment, the controller (408) detects whether the unavailability period has been activated by the UE (102) through a de-registration procedure between the UE (102) and the AMF apparatus (104).

[0465] In an embodiment, the controller (408) determines whether the UE (102) comes out of the unavailability period. The controller (308) then activates the AS layer (102B) of the UE (102) when the UE (102) comes out of the unavailability period.

[0466] In an embodiment, the controller (408) transmits an initial registration request message to the AMF apparatus (104) for initiating the initial registration procedure upon activation of the AS layer (102B). The UE (102) performs the initial registration procedure when the unavailability period is activated through the de-registration procedure. The UE (102) activates the unavailability period using the registration procedure and deactivates the AS layer (102B) only after the unavailability period has been activated. Further, the UE (102) activates the unavailability period using the de-registration procedure and deactivates the AS layer (102B) only after the unavailability period has been activated.

[0467] FIG. 5 is a block diagram that illustrates a schematic of the network apparatus (106) implemented to carry out the disclosed subject matter according to an embodiment as disclosed herein. For instance, the network apparatus (106) may also be referred to as the AMF apparatus (104), the mobility management entity (MME), a session management function (SMF), or any network function entity. As shown, the network apparatus (106) includes the processor (502), the memory (504), the I / O interface (506), and a timer controller (510). The timer controller (510) communicates with the I / O interface (506) and the memory (504). The timer controller (510) may be communicatively coupled to the memory (504) and the processor (502). The timer controller (510) is an innovative hardware that is realized through the physical implementation of both analog and digital circuits, including logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive and active electronic components, as well as optical components.

[0468] In an embodiment, the timer controller (510) receives unavailability information from the UE (102) through a registration procedure or an attach procedure or a Tracking Area Update (TAU) procedure or any during AS or NAS signaling procedure between the UE (102) and the network apparatus (106). For instance, the unavailability information includes at least one of a start of the unavailability period, an unavailability period duration, and an unavailability type. The term "unavailability period duration" refers to the amount of time that the UE (102) is not able to access network services or to a duration in which the Network is not available for the UE. The unavailability type may refer to a categorization of the duration during which the UE (102) or the Network is unavailable for communication. These types are used to classify the nature of the unavailability based on the underlying cause or context. For example, the unavailability type may include, but not limited to radio link failure (RLF) unavailability, handover failure unavailability, power saving unavailability, network unavailability, unavailability due to discontinuous coverage, unavailability due to UE reasonsand the like.

[0469] In an embodiment, the timer controller (510) determines a discontinuous coverage maximum time offset for the UE (102). The discontinuous coverage maximum time offset refers to the maximum time interval that the UE has to wait before UE can initiate a signaling or a communication with the Network upon returning to coverage after being out of coverage due to discontinuous coverage. The discontinuous coverage maximum time offset is crucial in scenarios where the UE (102) experiences intermittent connectivity, such as in areas with patchy coverage or when moving between cells or when the Network is available during certain duration and is unavailable at other time durations (for e.g. due to discontinuous coverage of the Network or the satellite network). If the UE (102) loses coverage, the UE has to wait for this maximum time offset duration (for e.g run a random timer not more than discontinuous coverage maximum time offset after coming out of discontinuous coverage and wait for the timer to expire) before the session or the signaling or communication can typically resume with the Network without interruption. However, if the UE (102) remains out of coverage for longer than a specified time (for e.g. more than the periodic registration or TAU timer or more than the mobile reachable timer or implicit detact / deregistration timer , the session may be dropped, requiring re-establishment of the connection when the UE (102) regains coverage. Further, the unavailability type is set to unavailability based on the discontinuous coverage.

[0470] In an embodiment, the timer controller (510) determines a value of a plurality of timers associated with the UE (102) based on the discontinuous coverage maximum time offset for the UE (102) determined. For instance, the timers may include, but not limited to a periodic tracking area update timer (T3412), an T3412 Extended Value or an extended T3412 timer, a mobile reachable timer, an implicit detach timer, a periodic registration update timer (T3512), an implicit de-registration timer, a plurality of negotiated extended DRX parameters, a plurality of extended idle mode DRX cycle parameters, an active Timer (T3324), a MICO mode (Mobile initiated connection only) configuration timer, an extended connected timer, a plurality of Power saving mode (PSM) mode configuration parameters, a T3324 Extended Connected time timer, and the like.

[0471] For instance, the T3412 timer controls the periodic tracking area update (TAU) or periodic location update (PLU) interval. It defines how long the UE (102) can stay registered in the network before sending an update to its current location. The T3512 timer controls the duration the UE (102) waits before initiating a periodic registration to the network. The T3324 manages the active timer which controls the duration till which the Network can page the UE after which the UE can enter power saving mode, optionally for the UE(s) operating in MICO mode.

[0472] In an embodiment, the timer controller (510) handles the plurality of timers based on the start of the unavailability period, the unavailability period duration, and the discontinuous coverage maximum offset. The timer controller (510) adjusts the discontinuous coverage maximum offset, based on a pre-determined plurality of timers, the start of the unavailability period, and the unavailability period duration. Adjusting the timer and parameters values for the plurality of timers defined herein or the discontinuous coverage maximum offset may be necessary and advantageous for improving user experience and network performance. For instance, increasing or decreasing the timer or parameters values (for e.g. based on the values of the unavailability period duration (if available), a start of unavailability period (if available) and a discontinuous coverage maximum time offset (if available)) may enable the UE (102) to remain registered / attached with the Network during brief coverage gaps, reducing the likelihood of the UE getting detached / deregistered from the Network. Adjusting the timer values or parameters or the maximum offset allows the network apparatus (106) to better manage resources, ensuring that the UE (102) remains registered / attached during brief coverage losses.

[0473] FIG. 6 is a sequence diagram that illustrates the unavailability through a registration procedure according to the embodiment as disclosed herein. As shown in the sequence diagram, the UE (102) is in communication with the AMF apparatus (104).

[0474] At step S1, an event of a trigger unavailability period occurs in the UE (102). At step S2, the AMF apparatus (104) transmits a registration accept message to the UE (102). At step S3, the UE (102) enters 5GMM-REGISTERED.NO-CELL-AVAILABLE state. At step S4, after NAS layer (102A) deactivates or disables the AS layer (102B) when the UE (102) enters 5GMM-REGISTERED.NO-CELL-AVAILABLE state. At step S5, the UE (102) comes out of the unavailability period or the unavailability period duration has expired. At step S6, the NAS layer (102A) activates the AS layer (102B) once the UE (102) has come out of the unavailability period.

[0475] The AS layer (102B) shall search the cell / PLMN and camp on it and indicate the result to the NAS layer (102A). In an embodiment, in step S5, the NAS layer (102A) that activates the AS layer (102B) also enters the state 5GMM-REGISTERED.PLMN-SEARCH.

[0476] In an embodiment, if the UE (102) doesn't deactivate the AS layer (102B) in steps S4 and S5, the NAS layer (102A) enters the state 5GMM-REGISTERED.PLMN-SEARCH.

[0477] In an embodiment, the UE (102) ignores all the indications from the AS layer (102B) after step S3. When the UE (102) comes out of the unavailability period or the unavailability period duration is expired, then the UE (102) enters 5GMM-REGISTERED.PLMN-SEARCH and start using the indication from the AS layer (102B).

[0478] FIG. 7 is a sequence diagram that illustrates the unavailability through the de-registration procedure according to the embodiment as disclosed herein. As shown in the sequence diagram, the UE (102) is in communication with the AMF apparatus (104).

[0479] At step S1, an event of a trigger unavailability period occurs in the UE (102). At step S2, the UE (102) receives a deregistration accept message from the AMF apparatus (104). At step S3, the UE (102) enters 5GMM-DEREGISTERED.NO-CELL-AVAILABLE state. At step S4, the NAS layer (102A) deactivates or disables the AS layer (102B) when the UE (102) enters 5GMM-DEREGISTERED.NO-CELL-AVAILABLE state. At step S5, the UE (102) comes out of the unavailability period or the unavailability period duration has expired. The NAS layer (102A) then activates the AS layer (102B) once the UE (102) has come out of the unavailability period. The AS layer (102B) shall search the cell / PLMN and camp on it and indicate the result to the NAS layer (102A).

[0480] In an embodiment, in step S5, the NAS layer (102A) that activates the AS layer (102B) also enters the state 5GMM-DEREGISTERED.PLMN-SEARCH.

[0481] In an embodiment, if the UE (102) doesn't deactivate the AS layer (102B) in steps S4 and S5, the NAS layer (102A) enters the state 5GMM-REGISTERED.PLMN-SEARCH.

[0482] In an embodiment, the UE (102) ignores all the indication from the AS layer (102B) after step S3. When the UE (102) comes out of the unavailability period or the unavailability period duration is expired, then the UE (102) enters 5GMM-REGISTERED.PLMN-SEARCH and searches for the suitable PLMN / cell and start using the indication from AS layer.

[0483] FIG. 8 is a scenario diagram that illustrates a scenario in which the UE (102) is not de-registered / detached by the network apparatus (106) according to the embodiment as disclosed herein. For instance, the network apparatus (106) may also be referred to as the AMF apparatus (104), the mobility management entity (MME), a session management function (SMF), or any network function entity. Since the UE (102) is not de-registered / detached by the network apparatus (106), the network apparatus (106) adjusts at least one of the timer T3512, the periodic update timer, the periodic registration timer, the timer T3412, the mobile reachable timer, the implicit de-registration / detach timer value, an T3412 Extended Value or an extended T3412 timer, a plurality of negotiated extended DRX parameters, a plurality of extended idle mode DRX cycle parameters, an active Timer (T3324), a MICO mode (Mobile initiated connection only) configuration timer, an extended connected time, a plurality of Power saving mode (PSM) mode configuration parameters, and a T3324 Extended Connected time timer, a discontinuous coverage maximum time offset and the maximum time offset value.

[0484] In an embodiment, the terms Maximum time offset value, maximum time offset, the discontinuous coverage maximum NAS signaling wait time and discontinuous coverage maximum time offset are used interchangeably and have the same meaning.

[0485] The network apparatus (106) may set the value of implicit de-registration timer or the implicit detach timer for the UE (102) considering the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signaling wait time or discontinuous coverage maximum time offset or any such name) (if available) along with the unavailability period duration (if available) and start of unavailability period (if available) provided / indicated by the UE (102) or determined by the network apparatus (106). This enables the sum of periodic update timer (or Periodic Registration Timer or Periodic TAU timer) and implicit de-registration / detach timer value to be more than (or optionally at least equal) to the sum of unavailability period and maximum time offset value provided to the UE (102) by the network apparatus (106).

[0486] In an embodiment, the network apparatus (106) may modify or determine the values of the periodic registration update / TAU timer considering the start of unavailability period, unavailability period duration, and maximum time offset value provided to the UE (102) (for e.g. based on availability and values of these timers). This enables the sum of the periodic update timer and implicit de-registration timer value to be more than or equal to the sum of unavailability period and maximum time offset value provided to the UE (102).

[0487] For example, the Unavailability Period is 2 hours, and the network apparatus (106) has provided the maximum time offset as 10 min. The network apparatus (106) should update the Implicit de-registration / detach timer value so that sum of periodic registration update timer value and implicit de-registration / detach timer value (say sum is 2 hours 15 min) for the UE (102) is greater than sum of unavailability period duration and Maximum wait range (for example, 2 hours and 10 min). After coming out of the unavailability period or discontinuous coverage (for example, after 2 hours), if the periodic registration update timer or periodic TAU timer expires in 10 mins and if the UE (102) performs the periodic registration update / TAU procedure in 10 min after unavailability period ends (for example, 2 hours 10 min), the network apparatus (106) will still have UE context. For example, the network apparatus (106) would not have detached / deregistered the UE (102) and the periodic registration / TAU update performed by the UE (102) will be successful.

[0488] In an embodiment, the network apparatus (106) may consider the values of periodic update timer provided to the UE (102), the unavailability period duration, and start of unavailability period while calculating the Maximum time offset value for the UE (102). The network apparatus (106) adjusts the value of Maximum time offset provided to the UE (102) considering the Periodic update timer provided by the UE (102) and the implicit de-registration / Detach timer value set for the UE (102). This enables the sum of periodic update timer and implicit de-registration / detach timer value at the network apparatus (106) to be more than (or optionally equal to) the sum of unavailability period and maximum time offset value provided to the UE (102).

[0489] In an embodiment, the network apparatus (106) may take the Unavailability Period Duration (if available), Start of Unavailability Period (if available), and the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signaling wait time or any such name) into account when determining Periodic Registration Update timer value or Timer T3512 or Periodic Update Timer or Periodic Registration Timer value or Periodic TAU timer (or Timer T3412) or the values of the plurality of timers for e.g. a periodic tracking area update timer (T3412), an T3412 Extended Value or an extended T3412 timer , a mobile reachable timer, an implicit detach timer, a periodic registration update timer (T3512), an implicit de-registration timer, a plurality of negotiated extended DRX parameters, a plurality of extended idle mode DRX cycle parameters, an active Timer (T3324), a MICO mode (Mobile initiated connection only) configuration timer, an extended connected time, a plurality of Power saving mode (PSM) mode configuration parameters, and a T3324 Extended Connected time timer.

[0490] In an embodiment, the network apparatus (106) (for e.g. MME) may determine the values of the periodic tracking area update timer (T3412), extended idle mode DRX cycle parameters and PSM mode configuration parameters provided to the UE based on the discontinuous coverage maximum time offset, the unavailability period duration and the start of the unavailability period, if available

[0491] In an embodiment, during the registration procedure, the network apparatus (106) (for e.g. AMF) may determine the values of the negotiated extended DRX parameters, the timer T3324, and the periodic registration update timer (T3512) to be provided to the UE based on the discontinuous coverage maximum time offset, the unavailability period duration and the start of the unavailability period based on their availability

[0492] . The network apparatus (106) may provide a Periodic Registration Update time / Periodic TAU Timer longer than or equal to the combination of the Unavailability Period Duration, start of Unavailability Period, and Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signaling wait time or any such name) to avoid interfering with the UE (102) dealing with the event that causes the unavailability.

[0493] In an embodiment, during the registration / attach procedure, the network apparatus (106) may determine the value of the periodic registration update timer (T3512) or Periodic TAU timer (or Timer T3412) provided to the UE (102) based on the unavailability period duration (if available), the start of the unavailability period, and the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name) in such a way to avoid interfering with the UE (102) dealing with the event that causes the unavailability or to avoid deregistering / detaching the UE (102) while the UE (102) is in the unavailability period / discontinuous coverage.

[0494] In an embodiment, the network apparatus (106) should adjust the mobile reachable timer or Implicit Deregistration timer / Implicit Detach Timer or both, based on or considering the unavailability period duration (if available), the start of the unavailability period, and the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name) such that the network apparatus (106) does not implicitly deregister / detach the UE (102) while the UE (102) is unavailable.

[0495] In an embodiment, the network apparatus (106) may determine the periodic update timer / periodic TAU Timer value based on the stored value of the Unavailability period duration IE, or based on a network determined unavailability period duration when the Unavailability period duration IE is not provided by the UE (102), the start of the unavailability period (if available), and the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name).

[0496] In an embodiment, the network apparatus (106) may change / set / alter / indicate the value of any / at least one / or the combination of the Periodic Registration Update timer (or Timer T3512) or Periodic Update Timer or Periodic Registration Timer or Periodic TAU timer (or Timer T3412) or the mobile reachable timer or Implicit Deregistration timer or Implicit Detach timer or the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name) such that the network apparatus (106) does not implicitly deregister / detach the UE (102) while the UE (102) is unavailable or while the UE (102) is out of coverage.

[0497] If the UE (102) requests power saving features, the AMF apparatus (104) provides the UE (102) with timers (e.g., Periodic Registration Update timer), extended DRX in CM-IDLE configuration, and MICO mode configuration, a plurality of negotiated extended DRX parameters, a plurality of extended idle mode DRX cycle parameters, an active Timer (T3324), a MICO mode (Mobile initiated connection only) configuration timer, an extended connected time, a plurality of Power saving mode (PSM) mode configuration parameters, and a T3324 Extended Connected time timer.and to the NG-RAN Extended Connected Time, . The AMF apparatus (104) may also consider the Unavailability Period Duration (if available), Start of Unavailability Period (if available), and the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name). This is to keep the UE (102) in power saving mode and avoid the network apparatus (106) attempting to page the UE (102) if it is out of satellite network coverage. This shall ensure that the network apparatus (106) does not attempt to page the UE (102) even if the UE (102) is out of satellite network coverage or if the UE (102) is waiting for the discontinuous coverage wait timer / Maximum Waiting Time Offset / maximum time offset or the discontinuous coverage maximum NAS signalling wait time to expire.

[0498] In an embodiment, during Attach and TAU procedures, the MME allocates the periodic RAU / TAU timer value as periodic TAU timer to the UE (102) based on a VPLMN operator policy, low access priority indication from the UE (102), periodic RAU / TAU timer value requested by the UE (102), subscription information received from the HSS, and Start of Unavailability Period and / or Unavailability Period Duration and / or the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name), if using a RAN that provides discontinuous coverage.

[0499] In an embodiment, if the UE (102) requests power saving features, the MME provides the UE (102) with timers (e.g. periodic TAU timer, extended idle mode DRX, and PSM mode configuration). The MME may also consider the Unavailability Period Duration (if available), Start of Unavailability Period (if available), and the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name).

[0500] In an embodiment, the MME should adjust the mobile reachable timer or Implicit Detach timer or both, based on or considering the unavailability period duration (if available), the start of the unavailability period, and the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name) such that the MME does not implicitly detach the UE (102) while the UE (102) is out of coverage.

[0501] In an embodiment, the network apparatus (106) may indicate / decide / give different Periodic Registration Update timer (or Timer T3512) or Periodic Update Timer or Periodic Registration Timer or Periodic TAU timer (or Timer T3412) or use different mobile reachable timer or Implicit Deregistration timer or Implicit Detach timer for different UE(s). The network apparatus (106) doesn't give the Maximum time offset value (or maximum time offset or the discontinuous coverage maximum NAS signalling wait time or any such name) such that the periodic timer of UE (102) doesn't expire. The same timer (congestion or overload control is managed) and the network apparatus (106) does not implicitly deregister / detach the UE (102) while the UE (102) is unavailable or while the UE (102) is out of coverage.

[0502] In an embodiment, the UE (102) shall stop the discontinuous coverage maximum NAS signalling wait timer and initiate NAS signalling if the UE (102) receives a paging message, has pending emergency services, when the UE (102) enters a TAI outside the registration area, or the Periodic Registration Update timer (or Timer T3512) / Periodic TAU timer(or Timer T3412) expires. For example, the UE (102) would be allowed to initiate a NAS signalling towards the network apparatus (106) without waiting for the discontinuous coverage maximum NAS signalling wait timer to expire in such cases.

[0503] Case: The UE (102) may trigger MRU while MM BO is running:

[0504] The AMF apparatus (104) may detect 5GMM signalling congestion and perform general NAS level congestion control. Under the 5GMM signalling congestion conditions, the AMF apparatus (104) may reject 5GMM signalling requests (for example, Registration Request messages or Service Request messages) from the UE (102) with a Mobility Management Back-off Timer (for example, Timer T3346). While the Mobility Management back-off timer (MM BO Timer) (for example, Timer T3346) is running, the UE (102) may perform one or more of the below methods / procedures in any order or combinations:

[0505] - The UE (102), optionally supporting Discontinuous coverage functionalities, may initiate any AS or NAS signalling message (for example, Registration Request procedure / messages (for initial registration or mobility registration update procedures) or Service Request procedures) to indicate / negotiate to / with the network apparatus (106) regarding the discontinuous coverage period or UE out-of-coverage period or UE unavailability period when the UE (102) is about to lose coverage due to discontinuous coverage or before the UE (102) enters the discontinuous coverage;

[0506] - The UE (102), optionally, may not initiate any AS or NAS signalling message (for example, Registration Request / TAU request procedure / messages (for initial registration or mobility registration update procedures or TAU request) or Service Request procedures) to indicate / negotiate to / with the network apparatus (106) regarding the discontinuous coverage period or UE out-of-coverage period or UE unavailability period if the UE (102) determines that the unavailability period is small. For example, smaller than the MM Back-off timer or the unavailability period is lesser than the back off timer or the the unavailability period is less than the value or the sum of the values of the Back-off timer and / or implicit deregistration / detach timer / mobile reachable timer / periodic timer.

[0507] - The UE (102), optionally, may only initiate any AS or NAS signalling message (for example, Registration Request / TAU request procedure / messages (for initial registration or mobility registration update procedures or TAU request) or Service Request procedures) to indicate / negotiate to / with the network apparatus (106) regarding the discontinuous coverage period or UE out-of-coverage period or UE unavailability period if the UE (102) determines that the unavailability period is long i.e., during long unavailability period (for example, the cases like discontinuous satellite coverage) (or i.e., longer than the MM Back-off timer or the unavailability period is longer than the backoff timer or the the unavailability period is more than the value or the sum of the values of the Back-off timer and / or implicit deregistration / detach timer / mobile reachable timer / periodic timer).

[0508] - The UE (102), supporting Discontinuous coverage functionalities, may optionally provide / indicate "discontinuous coverage support" indication as part of 5GMM Core Network Capability in the Registration Request message for initial registration or mobility registration update.

[0509] - The UE (102) may optionally indicate the AS / NAS Mobility Management message (AS / NAS MM message) (for example, Registration Request message for initial registration / mobility registration update or Service Request message) for discontinuous coverage support / discontinuous coverage period or UE out-of-coverage period or UE unavailability period negotiation / indication is exempted from NAS congestion control. When the NAS MM congestion control is activated at the AMF apparatus (104), if the UE (102) indicates that the NAS MM message is exempted from NAS congestion control, the AMF apparatus (104) shall not reject the NAS MM message.

[0510] - The UE (102) may stop the Mobility Management back-off timer (MM BO Timer) (for example, Timer T3346), if running, before / after initiating the AS / NAS signalling message for discontinuous coverage support / period indication / negotiation.

[0511] In an embodiment, the UE (102) may continue to run the Mobility Management back-off timer (MM BO Timer) (for example, Timer T3346), if running, before / after initiating the AS / NAS signalling message for discontinuous coverage support / period indication / negotiation.

[0512] For example, the UE (102) gets a Mobility Management Back-off Timer (for example, Timer T3346) from the network apparatus (106) at 10am with a Timer value of 1 hour. The Implicit Deregistration timer may be set to a value of 1.5 hours. The UE (102) runs the Mobility Management Back-off Timer from 10AM to 11AM (for a duration of 1 hour). At 10.30AM, the UE (102) may be about to enter discontinuous coverage for 2 hours duration (10.30 AM -12.30PM). For example, the UE (102) has a long unavailability period, unavailability period might be a large value or the unavailability period is more than the value or the sum of the values of the Back-off timer and / or implicit deregistration / detach timer / mobile reachable timer / periodic timer. While the Mobility Management back-off timer (MM BO Timer) (for example, Timer T3346) (of duration 1 hour) is running, the UE (102), optionally supporting Discontinuous coverage functionalities, may optionally determine that the UE (102) has a long unavailability period (for example, longer than the MM Back-off timer or the unavailability period is longer than the back-off timer or the the unavailability period is more than the value or the sum of the values of the Back-off timer and / or implicit deregistration / detach timer / mobile reachable timer / periodic timer), may initiate any AS or NAS signalling message. For example, Registration Request procedure / messages (for initial registration or mobility registration update procedures) or Service Request procedures) to indicate / negotiate to / with the network apparatus (106) regarding the discontinuous coverage period or UE out-of-coverage period or UE unavailability period (for example, of duration 2 hours) when the UE (102) is about to lose coverage due to discontinuous coverage or before the UE (102) enters the discontinuous coverage.

[0513] The network apparatus (106) may configure / adjust the periodic registration timer and / or the Implicit Deregistration timer to be greater than 2 hours i.e., 2.5 hours or any value. For example, the discontinuous coverage period or the duration of the UE out-of-coverage period / UE expected unavailability duration as determined / indicated by the AMF apparatus (104) or indicated by the UE (102) or negotiated between the UE (102) and the AMF apparatus (104) or based on the satellite coverage availability information or by any method or parameter to avoid unintended implicit detach due to coverage gap.

[0514] For example, the network apparatus (106) may run / re-start an Implicit Deregistration timer for the UE (102) from 10.30AM with a duration of 2.5 hours (10.30AM-1PM). Since the UE (102) would enter discontinuous coverage and the network apparatus (106) is aware that UE (102) has entered discontinuous coverage, the network apparatus (106) shall not implicitly deregister / detach the UE (102). The UE (102) can trigger Mobility Registration Update or any AS / NAS signalling message once the UE (102) returns to coverage back from discontinuous coverage. The network apparatus (106) can adjust MM BO in such a way that the UE (102) can trigger MRU as MM BO finishes before Discontinuous Coverage (DC) starts:

[0515] In an embodiment, the network apparatus (106), optionally on determining that the UE (102) has a longer unavailability period ((for example, the cases like discontinuous satellite coverage) (or longer than the MM Back-off timer or the unavailability period is longer than the back-off timer or the the unavailability period is more than the value or the sum of the values of the Back-off timer and / or implicit deregistration / detach timer / mobile reachable timer / periodic timer), may adjust the Mobility Management back-off timer (MM BO Timer) (for example, Timer T3346) such that the UE (102) is allowed to trigger any AS / NAS signaling message. For example, Registration Request message for initial registration / mobility registration update or Service Request message to indicate / negotiate that to indicate / negotiate to / with the network apparatus (106) regarding the discontinuous coverage period or UE out-of-coverage period or UE unavailability period when the UE (102) is about to lose coverage due to discontinuous coverage or before the UE (102) enters the discontinuous coverage.

[0516] For example, if the UE (102) gets MM BO timer of value 1 hour and the UE (102) is about to enter discontinuous coverage after 30 minutes, then the MM BO timer can be adjusted by the network apparatus (106) to be less than 30 mins so that the UE (102) can indicate / negotiate to / to / with the network apparatus (106) regarding the discontinuous coverage period or UE out-of-coverage period or the UE unavailability period, when the UE (102) is about to lose coverage due to discontinuous coverage or before the UE (102) enters the discontinuous coverage. The UE (102) can trigger MRU (normal) and the network apparatus (106) can adjust MM BO in such a way that the UE (102) doesn't detach:

[0517] In an embodiment, the UE (102) may trigger a normal (i.e., not for discontinuous coverage support / coverage indication) Initial Registration / Mobility Registration Update procedure. If the network apparatus (106) detects 5GMM signaling congestion, the AMF apparatus (104) may reject 5GMM signaling requests (for example, Registration Request messages or Service Request messages) from the UE (102) and may include / configure / adjust a Mobility Management Back-off Timer (for example, Timer T3346) with a value to avoid unintended implicit detach of the UE (102) due to the coverage gap. The network apparatus (106) may decide the value of Mobility Management Back-off Timer (for example, Timer T3346) and / or the periodic registration timer and / or the Implicit Deregistration timer based on the discontinuous coverage period or the duration of the UE (102) out-of-coverage period / UE expected unavailability duration (as determined / indicated by the AMF apparatus (104) or indicated by the UE (102) or negotiated between the UE (102) and the AMF apparatus (104) or based on the satellite coverage availability information or by any method or parameter).

[0518] When the UE (102) indicates unavailability period, the network apparatus (106) shouldn't reject:

[0519] In an embodiment, if the UE (102) triggers an Initial Registration / Mobility Registration Update procedure / Service Request procedure or any AS / NAS signaling procedure with an indication of "Discontinuous Coverage Support" or any indication to indicate the discontinuous coverage period or UE out-of-coverage period or UE unavailability period and if the AMF apparatus (104) detects 5GMM signaling congestion, the AMF apparatus (104) shall not reject 5GMM signaling requests. For example, Registration Request messages or Service Request messages from the UE (102) and optionally, shall not include any Mobility Management back-off timer (MM BO Timer) (for example, Timer T3346). The network apparatus (106) shall consider that the NAS MM / SM message is exempted from NAS congestion control.

[0520] In an embodiment, the AMF apparatus (104) may detect 5GMM signaling congestion and perform general NAS level congestion control. Under the 5GMM signaling congestion conditions, the AMF apparatus (104) may reject 5GMM signaling requests from the UE (102). The AMF apparatus (104) should not reject requests for initial registration or mobility and periodic registration update or service request message, when "Discontinuous Coverage Support" or any indication to indicate the discontinuous coverage period or UE out-of-coverage period or UE unavailability period is indicated by the UE (102). When the UE (102) indicates unavailability period, the network apparatus (106) rejects in such a way that UE (102) doesn't detach:

[0521] In an embodiment, if the UE (102) triggers an Initial Registration / Mobility Registration Update procedure / Service Request procedure or any AS / NAS signaling procedure with an indication of "Discontinuous Coverage Support" or any indication to indicate the discontinuous coverage period or UE out-of-coverage period or UE unavailability period and if the AMF apparatus (104) detects 5GMM signaling congestion, the AMF apparatus (104) may reject 5GMM signaling requests, For example, Registration Request messages or Service Request messages from the UE (102) and may include / configure / adjust a Mobility Management Back-off Timer (for example, Timer T3346) with a value to avoid unintended implicit detach of the UE (102) due to coverage gap. The AMF apparatus (104) may decide the value of Mobility Management Back-off Timer (for example, Timer T3346) and / or the periodic registration timer and / or the Implicit Deregistration timer based on the discontinuous coverage period or the duration of the UE out-of-coverage period / UE expected unavailability duration (as determined / indicated by the AMF apparatus (104) or indicated by the UE (102) or negotiated between the UE (102) and the AMF apparatus (104) or based on the satellite coverage availability information or by any method or parameter).

[0522] FIG. 9 is a flow diagram that illustrates a method for handling the UE during the unavailability period through the registration procedure according to an embodiment as disclosed herein. The method includes steps (902-910). Each step is explained in further detail below.

[0523] At step (902), it is detected whether the unavailability period has been activated by the UE (102) through a registration procedure between the UE (102) and the AMF apparatus (104). The term "unavailability period" refers to the amount of time that the UE (102) is not able to access network services. For instance, the UE (102) may enter the　unavailability period　due to software upgrade or not in coverage of the satellite etc., and the like.

[0524] At step (904), the AS layer (102B) of the UE (102) is deactivated or disabled when the UE (102) is currently in the unavailability period. For instance, the AS layer (102B) may be deactivated by the NAS layer (102A) of the UE (102). The radio communication between the UE (102) and a radio access network (RAN) is handled by the AS layer (102B) of the UE (102). The radio interface's transmission, reception, and radio resource management are all handled by the AS layer (102B). The channels that transmit control messages and user data via the air interface are called radio bearers, and they are set up, maintained, and released by the AS layer (102B). The AS layer (102B) cannot carry out the aforementioned tasks while the UE (102) is unavailable due to deactivation of the AS layer (102B). This prevents the UE (102) from using too much battery life or power while it is unavailable.

[0525] At step (906), it is determined whether the UE (102) has come out of the unavailability period or the unavailability period duration has expired.

[0526] At step (908), the AS layer (102B) is activated when the UE (102) come out of the unavailability period. For instance, the AS layer (102B) may be reactivated by the NAS layer (102A). The UE (102) comes out of the unavailability period only when the AS layer (102B) is deactivated.

[0527] At step (910), a registration request message is transmitted to the AMF apparatus (104) for initiating the registration procedure for mobility and periodic registration update upon activation of the AS layer (102B). For example, the registration request message may include an identity of the UE (102), security capabilities of the UE (102), and other necessary information associated with the UE (102).

[0528] Fig. 10 is a flow diagram that illustrates a method for handling the UE (102) during the unavailability period through the de-registration procedure according to an embodiment as disclosed herein. The method includes steps (1002-1008). Each step is explained in further detail below.

[0529] At step (1002), it is detected whether the unavailability period has been activated by the UE (102) through a de-registration procedure between the UE (102) and the AMF apparatus (104).

[0530] At step (1004), it is determined whether the UE (102) has come out of the unavailability period or the unavailability period has expired.

[0531] At step (1006), the AS layer (102B) is activated when the UE (102) comes out of the unavailability period or the unavailability period has expired. For instance, the AS layer (102B) may be reactivated by the NAS layer (102A).

[0532] At step (1008), a registration request message is transmitted to the AMF apparatus (104) for initiating the registration procedure for initial registration upon activation of the AS layer (102B). Additionally, the AS layer (102B) is only deactivated when the unavailability period has been initiated by the UE (102) through the de-registration process.

[0533] In an embodiment, the UE (102) may come of unavailability period anytime by activating the AS layer (102B) and performing registration procedure for initial registration when unavailability period was activated using the de-registration procedure or registration procedure for Mobility and periodic registration update if unavailability period was activated using the registration procedure.

[0534] In an embodiment, when the UE (102) comes out of the unavailability period to resume normal services or the unavailability period duration has expired, the UE (102) will de-activate the unavailability period using the registration procedure for mobility and periodic registration procedure. The UE (102) shall then enter the sub state 5GMM-REGISTERED.PLMN-SEARCH.

[0535] In an embodiment, when the UE (102) comes out of the unavailability period to resume normal services or the unavailability period has expired, the UE (102) will de-activate the unavailability period using the registration procedure for initial registration. The UE (102) shall then enter the sub state 5GMM-DEREGISTERED.PLMN-SEARCH or 5GMM-DRREGISTERED.PLMN-SEARCH.

[0536] FIG. 11 is a flow diagram that illustrates a method for handling timers associated with the UE (102) during the unavailability period according to an embodiment as disclosed herein. The method includes steps (1102-1110). Each step is explained in further detail below. Each step can happen in any order or combination or in a any sequence.

[0537] At step (1102), unavailability information is received from the UE (102) through a registration or a Attach or a TAU or any AS or NAS signalling procedure between the UE (102) and the network apparatus (106). For instance, the unavailability information includes at least one of a start of the unavailability period, an unavailability period duration, and an unavailability type. "Unavailability period duration" describes the duration of time that the UE (102) cannot access network services. The term "unavailability type" might pertain to a classification of the time frame in which the UE　(102) or the Network is not reachable. These categories are used to categorize the type of unavailability according to the context or underlying reason. For example, the unavailability type may include, but not limited to radio link failure (RLF) unavailability, handover failure unavailability, power saving unavailability, network unavailability, unavailability due to discontinuous coverage, unavailability due to discontinuous coverage and the like.

[0538] At step (1104), a discontinuous coverage maximum time offset for the UE (102) is determined. The discontinuous coverage maximum time offset refers to the maximum time interval that the UE has to wait before UE can initiate a signaling or a communication with the Network upon returning to coverage after being out of coverage due to discontinuous coverage. When moving between cells or in locations with patchy coverage, for example, when the UE (102) has intermittent connectivity, or when the Network is available during certain duration and is unavailable at other time durations (for e.g. due to discontinuous coverage of the Network or the satellite network). the discontinuous coverage maximum time offset becomes critical. If the UE (102) loses coverage, the UE has to wait for this maximum time offset duration (for e.g run a random timer not more than discontinuous coverage maximum time offset after coming out of discontinuous coverage and wait for the timer to expire) before the session or the signaling or communication can typically resume with the Network without interruption. However, if the UE (102) remains out of coverage for longer than a specified time (for e.g. more than the periodic registration or TAU timer or more than the mobile reachable timer or implicit detact / deregistration timer, the session may be dropped, requiring re-establishment of the connection when the UE (102) regains coverage. Further, the unavailability type is set to unavailability based on the discontinuous coverage.

[0539] At step (1106), a value of a plurality of timers associated with the UE (102) is determined based on the discontinuous coverage maximum time offset for the UE (102) determined. For instance, the timers may include, but not limited to a periodic tracking area update timer (T3412), an T3412 Extended Value or an extended T3412 timer, a mobile reachable timer, an implicit detach timer, a periodic registration update timer (T3512), an implicit de-registration timer, a plurality of negotiated extended DRX parameters, a plurality of extended idle mode DRX cycle parameters,an active Timer (T3324), a MICO mode (Mobile initiated connection only) configuration timer, an extended connected timer, a plurality of Power saving mode (PSM) mode configuration parameters, a T3324 Extended Connected time timer, and the like.

[0540] At step (1108), the plurality of timers are handled based on the start of the unavailability period, the unavailability period duration, and the discontinuous coverage maximum offset. Handling the timers associated with the UE (102) is essential for ensuring efficient network operation, maintaining service continuity, and optimizing user experience. Proper handling of the timers ensures that the UE (102) may quickly recover from brief disconnections, thereby minimizing interruptions for ongoing services.

[0541] At step (1110), the discontinuous coverage maximum offset is adjusted based on a pre-determined plurality of timers, the start of the unavailability period, and the unavailability period duration. For better user experience and network performance, adjusting the discontinuous coverage maximum offset may be beneficial and essential. Increasing the time offset, for example, may allow the UE (102) to stay registered / attached during small coverage gaps, which would lower the chance of the UE (102) getting deregistered or deattached from the Network.. In order to ensure that the UE (102) stays registered / attached during temporary coverage losses, the network apparatus　(106) may　better manage resources by adjusting the offset.

[0542] The various actions, acts, blocks, steps, or the like in the method is performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like are omitted, added, modified, skipped, or the like without departing from the scope of the proposed method.

[0543] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.

Claims

1.A method performed by a terminal in a wireless communication system, the method comprising:identifying whether an unavailability period is activated;deactivating an access stratum (AS) layer of the terminal in case that the unavailability period is activated;determining whether the terminal comes out of the unavailability period;activating the AS layer of the terminal in case that the terminal comes out of the unavailability period; andperforming a registration procedure.2.The method of claim 1, wherein the performing further comprising:performing an initial registration, in case that the unavailability period is activated based on a de-registration procedure.3.The method of claim 1, further comprising:performing a mobility and period registration update procedure in case that the unavailability period is activated based on a registration procedure.4.The method of claim 1, wherein the unavailability period is activated based on a registration procedure, or a de-registration procedure.5.A method performed by a core network entity in a wireless communication system, the method comprising:identifying at least one of an unavailability period duration or a start of an unavailability period; anddetermining a periodic registration update timer value based on the at least one of the unavailability period duration or the start of an unavailability period.6.The method of claim 5, further comprising:determining at least one of a value of a negotiated extended DRX parameter, or a timer T3324, based on a registration procedure.7.The method of claim 5, wherein the core network entity comprises an access and mobility management function (AMF) entity or a mobility management entity (MME).8.A terminal in a wireless communication system, the terminal comprising:a transceiver; andat least one processor configured to:identify whether an unavailability period is activated,deactivate an access stratum (AS) layer of the terminal in case that the unavailability period is activated,determine whether the terminal comes out of the unavailability period,activate the AS layer of the terminal in case that the terminal comes out of the unavailability period, andperform a registration procedure.9.The terminal of claim 8, wherein the at least one processor is further configured to:perform an initial registration, in case that the unavailability period is activated based on a de-registration procedure.10.The terminal of claim 8, wherein the at least one processor is further configured to:perform a mobility and period registration update procedure in case that the unavailability period is activated based on a registration procedure.11.The terminal of claim 8, wherein the unavailability period is activated based on a registration procedure, or a de-registration procedure.12.A core network entity in a wireless communication system, the core network entity comprising:a transceiver; andat least one processor configured to:identify at least one of an unavailability period duration or a start of an unavailability period, anddetermine a periodic registration update timer value based on the at least one of the unavailability period duration or the start of an unavailability period.13.The core network entity of claim 12, wherein the at least one processor is further configured to:determine at least one of a value of a negotiated extended DRX parameter, or a timer T3324, based on a registration procedure.14.The core network entity of claim 12, wherein the core network entity comprises an access and mobility management function (AMF) entity or a mobility management entity (MME).

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